Functional Knockout of the Transient Outward Current, Long-QT Syndrome, and Cardiac Remodeling in Mice Expressing a Dominant-Negative Kv4 Subunit

From the Departments of Molecular Biology and Pharmacology (D.M.B., H.X., J.M.N.) and Surgery (R.B.S.), Washington University Medical School, St Louis, Mo.

Correspondence to Dr Jeanne M. Nerbonne, Department of Molecular Biology and Pharmacology, Washington University Medical School, 660 South Euclid Ave, St Louis, MO 63110. E-mail jnerbonn{at}pharmdec.wustl.edu

	Abstract

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Abstract—A novel in vivo experimental strategy, involving cell type–specific expression of a dominant-negative K⁺ channel pore-forming subunit, was developed and exploited to probe the molecular identity of the cardiac transient outward K⁺ current (I_to). A point mutation (W to F) was introduced at position 362 in the pore region of Kv4.2 to produce a nonconducting mutant (Kv4.2W362F) subunit. Coexpression of Kv4.2W362F with Kv4.2 (or Kv4.3) attenuates the wild-type currents, and the effect is subfamily specific; ie, Kv4.2W362F does not affect heterologously expressed Kv1.4 currents. With the use of the -myosin heavy chain promoter to direct cardiac-specific expression, several lines of Kv4.2W362F transgenic mice were generated. Electrophysiological recordings reveal that I_to is selectively eliminated in ventricular myocytes isolated from transgenic mice expressing Kv4.2W362F, thereby demonstrating directly that the Kv 4 subfamily underlies I_to in the mammalian heart. Functional knockout of I_to leads to marked increases in action potential durations in ventricular myocytes and to prolongation of the QT interval in surface ECG recordings. In addition, a novel rapidly activating and inactivating K⁺ current, which is not detectable in myocytes from nontransgenic littermates, is evident in Kv4.2W362F-expressing ventricular cells. Importantly, these results demonstrate that electrical remodeling occurs in the heart when the expression of endogenous K⁺ channels is altered.

Key Words: transgenic mouse • transient outward current • ventricle • action potential • long QT

	Introduction

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Voltage-gated K⁺ channels function to control the height and duration of the cardiac action potential, and in most myocardial cells, 2 broad classes of voltage-gated K⁺ currents have been identified: rapidly activating and inactivating, ie, transient K⁺ current (I_to) and delayed, slowly activating, outwardly rectifying K⁺ current (I_K).^{1 2 3} In addition to controlling action potential repolarization, I_to and I_K are important targets for the actions of endogenous transmitters and hormones as well as exogenous drugs, known to modulate cardiac functioning.¹ Changes in the properties and densities of voltage-gated K⁺ currents are seen in a variety cardiovascular disorders,^{4 5 6} and there is considerable interest in defining the molecular correlates of I_to and I_K and in understanding the mechanisms involved in the regulation, modulation, and functional expression of these channels.

Recently, 2 K⁺ channel genes, KvLQT1⁷ and human ether-a-go-go (or HERG)⁸ have been identified as the loci of mutations in 2 forms of familial long-QT syndrome. HERG underlies I_Kr (the rapid I_K) in cardiac cells,^{9 10} whereas KvLQT1 contributes to I_Ks (the slow I_K).^{11 12} In contrast to the functional and molecular diversity of I_K, the properties of I_to in adult mammalian cardiac cells isolated from different species, as well as from different regions of the heart in the same species, are quite similar, suggesting that the molecular correlates of I_to in different species and cell types are likely the same.¹ Previous biochemical, molecular, and pharmacological studies have suggested alternatively that members of the Shal (Kv 4)^{13 14 15 16 17 18} or the Shaker (Kv 1)^{19 20} subfamilies of voltage-gated K⁺ channel (Kv) subunits contribute to I_to in mature myocardial cells.

The experiments in the present study were undertaken to test directly the hypothesis that members of the Kv4 subfamily underlie I_to in the mammalian heart and to determine the physiological consequences of the functional knockout of I_to on myocardial excitability. To achieve this, a point mutation was introduced in the pore region of Kv4.2 to produce a subunit (Kv4.2W362F) that functions as a dominant negative.^{21 22} Transgenic mice expressing Kv4.2 driven by the -myosin heavy chain promoter^{23 24 25 26} were then generated and characterized. Electrophysiological studies reveal that I_to is selectively eliminated in ventricular myocytes isolated from Kv4.2W362F-expressing mice, demonstrating that the Kv4 subfamily underlies I_to in the mammalian heart. In addition, functional knockout of I_to leads to marked increases in action potential durations in ventricular myocytes and to prolongation of the QT interval.

	Materials and Methods

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Construction of the Epitope-Tagged Dominant-Negative Kv4.2, Kv4.2W362F-FLAG
Inverse polymerase chain reaction was used to introduce mutations in the DNA sequence encoding the pore region of Kv4.2; pRc/CMV-Kv4.2 was obtained from Drs Morgan Sheng and Lily Jan (University of California at San Francisco). The mutations had 2 functions: (1) to introduce the SacII restriction enzyme site (without altering the amino acid sequence) and (2) to alter the amino acid sequence at position 362 in the pore region from W (tryptophan [W]) YT to F (phenylalanine [F]) YT (designated W362F). The 6.5-kb polymerase chain reaction fragments were electrophoresed through 1% agarose gel and extracted. Plasmid DNA was isolated, and restriction enzyme digests were performed to identify plasmids that contained the mutation; those positive for the SacII site were sequenced. In addition, the stop codon was removed, and Kv4.2W362F was tagged at the C terminus with the 8–amino acid FLAG epitope. Oligonucleotides were generated by the Protein and Nucleic Acid Chemistry Laboratory (Washington University, St Louis, Mo).

Generation of Transgenic Mice Expressing -MHC–Kv4.2W362F-FLAG
The Kv4.2W362F-FLAG coding sequence was subcloned into the -myosin heavy chain (-MHC) vector^{23 24 25 26} at the SalI site. The -MHC–Kv4.2W362F plasmid was digested to isolate a 7-kb fragment that included the -MHC promoter, the first 3 noncoding exons of the -MHC gene, the Kv4.2W362F-FLAG coding sequence, and the human growth hormone (HGH) polyadenylation signal sequences.^{23 24 25 26} After purification, this fragment was resuspended in 100 µL of 10 mmol/L Tris buffer containing 10 mmol/L NaCl and 0.1 mmol/L EDTA at pH 7.4 and dialyzed against a 0.1-µm Millipore filter. The fragment was then diluted to a concentration of 1 ng/µL and injected into 100 fertilized C57CBA mouse oocytes. After the injections, the oocytes were transplanted into pseudopregnant C57CBA adult mice. A total of 57 offspring were obtained, and all were screened for expression of the transgene by Southern blot analysis of (tail) genomic DNA; a probe directed against the HGH polyadenylation sequence (in the -MHC vector^23–26) was used to assay for transgene expression. Briefly, genomic DNA was isolated, digested with EcoRI, and electrophoresed through a 1% agarose gel. The gel was then treated sequentially with 0.25 mol/L HCl for 25 minutes, denaturing buffer (0.5 mol/L NaOH and 1.5 mol/L NaCl) for 1 hour, and then neutralization buffer (0.1 mol/L Tris containing 1.5 mol/L NaCl at pH 7.5). The DNA was then transferred from the gel to Magnacharge nylon membrane (MSI Separations), and the membranes were incubated with a radiolabeled probe directed against the HGH polyadenylation sequences overnight at 42°C. After repeated washings, the membranes were exposed to film for 2 to 5 days at -80°C; the films were then developed, and the 3 animals positive for the transgene were identified (see Results).

Cell Lines and Transient Transfections
QT-6 cells (a quail fibroblast cell line), originally obtained from the laboratory of Dr John Merlie (Washington University Medical School, St Louis, Mo) and maintained as described previously,¹⁴ were transiently transfected by the calcium phosphate method¹⁴ with plasmids encoding Kv4.2, Kv4.3, or Kv4.2W362F together with green fluorescent protein (pGREENLANTERN, GIBCO BRL) to allow transfected cells to be identified before electrophysiological recordings.

Expression of Kv4.2W362F in Transgenic Mice
Ventricular myocytes were isolated from adult transgenic and wild-type mice by use of a protocol similar to one previously described for isolation of rat cardiocytes.¹⁶ To assay FLAG expression, cells were fixed in 4% paraformaldehyde in 0.1 mol/L PBS at pH 7.4 for 1 hour. After a 1-hour incubation in blocking buffer (PBS containing 5% normal goat serum, 0.2% Triton X-100, and 0.1% NaN₃), cells were incubated overnight at 4°C with the anti-FLAG M2 antibody (Eastman Kodak) diluted 1:500 in blocking buffer. After they were washed with PBS, cells were then exposed for 1 hour at room temperature to a Cy3-conjugated goat anti-mouse secondary antibody (Chemicon) diluted 1:1000 in blocking buffer; labeling was visualized under epifluorescence illumination.

Mouse ventricular membrane proteins were prepared using a protocol previously developed for the isolation of rat cardiac membrane proteins.^{14 16} After fractionation by SDS-PAGE and transfer to polyvinylidene fluoride membranes (Amersham), immunoblots were completed with the anti-FLAG M2 antibody diluted 1:500, followed by an alkaline phosphatase–conjugated goat anti-mouse secondary antibody (Tropix). Bound antibodies were detected using the CPSD (Tropix) chemiluminescent alkaline phosphatase substrate.^{14 16}

Electrophysiological Recordings
Whole-cell voltage-clamp recordings from green fluorescent protein–positive QT-6 cells were obtained at room temperature 48 hours after transfections. The recording pipettes contained (mmol/L) KCl 115, KOH 15, EGTA 10, HEPES 10, and glucose 5 (pH 7.2, 300 to 310 mOsm). The bath solution contained (mmol/L) NaCl 140, KCl 4, MgCl₂ 2, CaCl₂ 1, HEPES 10, and glucose 5 (pH 7.4, 300 to 310 mOsm). Experiments were performed by using a Dagan model 3900 patch-clamp amplifier interfaced to an IBM-compatible 486 computer with a Tecmar Labmaster-1 analog/digital interface (Axon Instruments) and the pClamp 6 software package (Axon). Data were filtered at 5 kHz before storage. Electrodes were fabricated from soda lime glass (Kimble), coated with Sylgard (Dow Corning), and fire-polished; tip resistances were 1.5 to 2.5 M. Series resistances were in the range of 3 to 4 M and were compensated electronically by 80% to 90%; voltage errors resulting from the uncompensated series resistance were 8 mV and were not corrected.

Recordings from isolated ventricular myocytes were obtained at room temperature on the day of isolation. The recording conditions were the same as those described above for experiments on QT-6 cells, except as noted. For voltage-clamp experiments, the bath solution routinely contained (mmol/L) NaCl 136, KCl 4, CaCl₂ 1, MgCl₂ 2, CoCl₂ 5, HEPES 10, glucose 10, and tetrodotoxin 0.02 (pH 7.4, 295 to 300 mOsm); tetrodotoxin and Co²⁺ were eliminated when action potentials were recorded. For both current- and voltage-clamp experiments, the recording pipette solution contained (mmol/L) KCl 135, EGTA 10, HEPES 10, and glucose 5 (pH 7.2, 295 to 310 mOsm). Outward K⁺ currents were evoked during 200-ms or 3-s depolarizing voltage steps to test potentials between -50 and +50 mV from a holding potential of -70 mV after a 20-ms prepulse to -20 mV (to eliminate the tetrodotoxin-insensitive voltage-gated Na⁺ current). Inwardly rectifying K⁺ current (I_K1) was evoked during hyperpolarizing voltage steps to test potentials between -90 and -130 mV. Electrodes, fabricated as described above, had tip resistances of 1.5 to 2.0 M when filled with the standard recording solution. Series resistances were in the range of 3 to 3.5 M and were compensated electronically by 80% to 90%; voltage errors resulting from the uncompensated series resistance were always 6 mV and were not corrected.

Electrocardiograms
Surface ECGs were recorded from adult wild-type and Kv4.2W362F-expressing mice by using methods similar to those previously described.²⁷ Briefly, mice were lightly anesthetized with 3% halothane (97% O₂), and needle electrodes were placed on the limbs under the skin. Standard ECG recordings were first obtained from leads I, II, and III simultaneously at a frequency response of 0.05 to 500 Hz with the use of a Gould model 13-4615 ECG amplifier (Gould Inc). The electrode normally on the left arm was then moved to the back of the left shoulder, and the right arm electrode was placed at the base of the sternum. In this configuration, maximal amplitude recordings were obtained, facilitating the resolution of the QT wave(s) and, therefore, allowing more accurate measurements of QT intervals. Signals were digitized at 2 kHz and recorded on a 486 personal computer.

Data Analysis
Voltage-clamp and current-clamp data were compiled and analyzed using Clampfit (Axon Instruments) and Excel (Microsoft). For each cell, the spatial control of the membrane voltage was assessed by analyzing the decays of the capacitative transients evoked during subthreshold ±10-mV voltage steps from the holding potential (-70 mV); only cells with capacitative transients well described by single exponentials were analyzed further. Whole-cell ventricular myocyte membrane capacitances were determined by integration of the capacitative transients evoked during brief (25-ms) subthreshold (±10-mV) voltage steps from a holding potential of -70 mV. The whole-cell membrane capacitances of cells isolated from wild-type and transgenic animals were indistinguishable, with mean±SEM values of 140±8 pF (n=20) and 152±9 pF (n=35) in wild-type and Kv4.2W362F-expressing cells, respectively. The input resistances of adult mouse wild-type (n=15) and Kv4.2W362F-expressing (n=22) ventricular myocytes were also indistinguishable, with mean±SEM values of 1.33±0.22 G and 1.47±0.30 G, respectively. Leak currents were always <100 pA and were not corrected. The plateau outward K⁺ current was defined as the current remaining 3 s after the onset of the depolarizing voltage steps, and the peak outward current was defined as the maximum value of the outward K⁺ current during 200-ms voltage steps. Current amplitudes, measured in individual cells, were normalized for differences in cell size (whole-cell membrane capacitance), and current densities (in pA/pF) are reported.

The time constants of inactivation of the depolarization-activated outward K⁺ currents in wild-type and Kv4.2W362F-expressing ventricular myocytes were determined from double-exponential fits to the decay phases of the current, using the following equation: A_t=A₁ · exp(-t/₁)+A₂ · exp(-t/₂)+A_ss, where A_t is the amplitude of the current at time, t; A₁, ₁, A₂, and ₂ represent the amplitudes (A) and the time constants () of the fast (subscript 1) and slow (subscript 2) components of current decay; and A_ss is the amplitude of the noninactivating component of the total outward K⁺ current. In some analyses, the decay phases of the currents in wild-type ventricular myocytes were (force) fitted by the sum of 3 exponentials with fixed time constants (see Results). In this case, a third current component (A₃) with a decay time constant (₃) of 200 ms was added; the values of ₁ (I_to) and ₂ (the slow current) were also fixed at 70 ms and 1000 ms, respectively (see Results). Correlation coefficients were determined to assess the quality of the fits; in all cases, correlation coefficients were 0.980. For analysis of ECGs, the onsets and offsets of the P, Q, R, S, and T waves were determined by measuring the earliest (onset) and the latest (offset) times from the 3 leads. Measured QT intervals were corrected for differences in heart rate using the formula, QTc=QT/(RR/100)^1/2, as described by London et al.²⁸ All data are presented as mean±SEM. Differences between wild-type and Kv4.2W362F-expressing myocytes were analyzed using ANOVA and the Student t test; P values are presented in the text.

	Results

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Generation and Characterization of the Dominant-Negative Kv4.2 Construct, Kv4.2W362F
To generate the Kv4 dominant-negative construct, mutations were introduced to the cDNA sequence to change the tryptophan (W) residue at position 362 in the pore region of Kv4.2 to phenylalanine (F). This mutation is analogous to ones made in Shaker²¹ and Kv1.1²² that were demonstrated to produce K⁺ channels that gate on membrane depolarization but do not conduct. The dominant-negative Kv4 construct is referred to as Kv4.2W362F (Figure 1a). Because Kv4 -subunit expression is readily detected in mouse ventricles by Western blot analysis and by immunohistochemistry (data not shown), the dominant-negative Kv4 subunit was tagged at the C-terminus with the 8 amino acid FLAG epitope to allow direct detection of expression of the transgene (see Materials and Methods).

View larger version (29K): [in this window] [in a new window]   Figure 1. Kv4.2W362F functions as a dominant-negative subunit. a, Predicted membrane topology of the Kv4.2 subunit with the point mutation in the pore region (H5) indicated by the arrowhead; the 6 transmembrane domains (S1–S6) are boxed. b to h, Whole-cell outward K+ currents recorded from transiently transfected QT-6 cells. Currents were evoked during 150-ms depolarizing voltage steps to potentials between -50 and +60 mV from a holding potential of -70 mV. No outward K+ currents are recorded from QT-6 cells expressing Kv4.2W362F (b). Coexpression of Kv4.2W362F with the wild-type Kv4 subunits, Kv4.2 (d) or Kv4.3 (f), however, markedly reduces (d, Kv4.2) or abolishes (f, Kv4.3) the outward K+ currents seen on expression of Kv4.2 (c) or Kv4.3 (e) alone. The currents recorded in QT-6 cells cotransfected with Kv1.4 and Kv4.2W362F (h) are indistinguishable from those recorded from cells expressing Kv1.4 alone (g). Scale bars are 2 nA and 20 ms.

When transiently transfected into QT-6 cells, expression of Kv4.2W362F was readily detected immunohistochemically using either an anti-Kv4.2 antibody or an anti-FLAG M2 antibody (data not shown). In whole-cell voltage-clamp recordings from Kv4.2W362F-FLAG–expressing QT-6 cells, however, no outward K⁺ currents were recorded (Figure 1b), suggesting that the mutant Kv4 subunit forms channels that are nonconducting. Furthermore, when equal amounts of the plasmids encoding wild-type Kv4.2 and Kv4.2W362F-FLAG were cotransfected into QT-6 cells, the densities of the Kv4.2-induced currents are markedly reduced (Figure 1d) compared with cells expressing wild-type Kv4.2 alone (Figure 1c). The mean±SEM peak outward K⁺ current densities at +50 mV in QT-6–expressing wild-type Kv4.2 alone or wild-type Kv4.2 plus Kv4.2W362F were 454±36 pA/pF (n=10) and 87±16 pA/pF (n=10), respectively; these values are significantly (at the P<0.001 level) different. However, the voltage dependences and the rates of activation and inactivation of the Kv4.2-induced currents in the absence and in the presence of Kv4.2W362F are indistinguishable (n=10), indicating that assembly of wild-type subunits with Kv4.2W362F leads to nonfunctional channels rather than to channels with altered time- and/or voltage-dependent properties; ie, Kv4.2W362F functions as a dominant negative.^{21 22}

Coexpression of Kv4.2W362F with another member of the Kv4 subfamily, Kv4.3, also attenuates the K⁺ currents (Figure 1f) produced on expression of Kv4.3 alone (Figure 1e). The mean±SEM peak outward K⁺ current density at +50 mV in QT-6–expressing wild-type Kv4.3 was 351±76 pA/pF (n=10), and no outward K⁺ currents were recorded from cells coexpressing wild-type Kv4.3 and Kv4.2W362F. However, coexpression of Kv4.2W362F with Kv1.4, a member of the Shaker subfamily that is not expected to assemble with subunits of the Kv4 subfamily,²⁹ has no measurable effect on Kv1.4 currents (Figure 1g and 1h). The mean±SEM peak outward K⁺ current densities at +50 mV in QT-6–expressing Kv1.4 alone or Kv1.4 plus Kv4.2W362F were 476±75 pA/pF (n=9) and 432±79 pA/pF (n=9), respectively; these values are not significantly different.

Generation and Characterization of Transgenic Mice Expressing Kv4.2W362F
The FLAG-tagged Kv4.2W362F DNA sequence was subcloned (see Materials and Methods) downstream from the cardiac-specific -MHC promoter in the -MHC expression vector (generously provided to us by Dr Jeffery Robbins, University of Cincinnati, Cincinnati, Ohio). Previous work has documented that this promoter is cardiac specific and that constitutive expression of the -MHC protein, as well as transgenes driven by this promoter, are detected in atria and ventricles from the time of birth.^{23 24 25 26} A 7-kb fragment containing the -MHC promoter, the Kv4.2W362F-FLAG sequence, and the HGH polyadenylation signal sequence was isolated and injected into fertilized mouse oocytes (see Materials and Methods). For screening, genomic tail DNA was prepared, and transgene incorporation was assayed by Southern blot analysis using a probe directed against the HGH polyadenylation signal sequence (see Materials and Methods). Three founders (Nos. 15, 25, and 27) were identified (data not shown) and were bred to wild-type C57CBA mice to generate 3 lines of Kv4.2W362F-FLAG–expressing transgenic mice. Initial analysis of the functional consequences of Kv4.2W362F expression were completed on the F1 progeny of founder No. 25. As illustrated in Figure 2a, Kv4.3W362F-FLAG protein expression was readily detected in Western blots of fractionated mouse ventricular membrane proteins prepared from line 25 transgenic animals (Figure 2a, arrow), whereas nothing is detected in immunoblots of ventricular membrane proteins prepared from wild-type littermates. In addition, the FLAG epitope was readily detected immunohistochemically in isolated ventricular myocytes from transgenic animals (Figure 2b and 2c), whereas no staining was observed in myocytes isolated from nontransgenic littermates (Figure 2d and 2e).

View larger version (53K): [in this window] [in a new window]   Figure 2. Kv4.2W362F-FLAG is readily detected in ventricular myocytes of transgenic animals. a, Mouse ventricular membrane proteins were prepared from wild-type (WT) and transgenic (T) ventricles, separated by SDS-PAGE, and blotted with the anti–FLAG M2 antibody (see Materials and Methods). A prominent band, corresponding to Kv4.2W362F-FLAG, is readily detected in membrane proteins prepared from T ventricles (arrow), whereas Kv4.2W362F-FLAG is not detected in immunoblots of fractionated WT ventricular membrane proteins. b and d, Phase-contrast images of typical ventricular myocytes isolated from T (b) and WT (d) littermates are shown. c and e, The same fields (as in panels b and d) were photographed under epifluorescence illumination. The FLAG epitope is readily detected in the myocytes isolated from Kv4.2W362F-expressing animals (c), whereas no staining was apparent in WT cells (e).

On gross examination, there are no obvious differences between the Kv4.2W362F-expressing transgenic animals and their nontransgenic littermates. Mean±SEM body weights, for example, were 25.1±4.4 g (n=5) and 26.3±2.5 g (n=10) for 8-week (adult) wild-type and Kv4.2W362F-expressing animals; these values are not significantly different. Heart weights were also not significantly different, with mean±SEM values of 98±9 mg (n=5) and 102±7 mg (n=10) for wild-type and Kv4.2W362F-expressing animals, respectively. Heart weight–to–body weight ratios in nontransgenic and transgenic animals were also very similar, and histological examination of hearts from Kv4.2W362F-expressing animals revealed no significant differences from control hearts. In addition, the input resistances and whole-cell membrane capacitances of ventricular myocytes isolated from Kv4.2W362F-expressing and wild-type animals are indistinguishable (see Materials and Methods).

Outward K⁺ Currents Are Altered in Kv4.2W362F-Expressing Ventricular Myocytes
Whole-cell voltage-clamp recordings, however, revealed marked differences in the waveforms of the depolarization-activated outward K⁺ currents in ventricular myocytes isolated from wild-type and transgenic littermates (Figure 3). As illustrated in Figure 3, peak outward K⁺ current amplitudes at all test potentials are substantially lower in cells isolated from transgenic animals (Figure 3b and 3d) compared with the currents typically recorded in myocytes isolated from wild-type littermates (Figure 3a and 3c). Similar results were obtained in 40 myocytes from 2 Kv4.2W362F-FLAG transgenic animals derived from line 25, and the mean±SEM peak outward densities at +20 mV were 37.1±2.5 pA/pF (n=39) and 16.1±1.0 pA/pF (n=40) in wild-type and Kv4.2W362F-expressing myocytes, respectively; these values are significantly (at the P0.001 level) different. In contrast to the marked reductions in peak outward K⁺ current densities in ventricular myocytes isolated from the Kv4.2W362F-expressing transgenic animals, no measurable effects on the densities of either the plateau outward K⁺ currents, determined as the currents remaining at the end of 3-s voltage steps, or of the hyperpolarization-activated inwardly rectifying K⁺ current, I_K1, were observed. Mean±SEM plateau outward current densities at +20 mV, for example, were 3.5±0.4 pA/pF (n=18) and 3.7±0.2 pA/pF (n=18) in wild-type and Kv4.2W362F-expressing myocytes, respectively (Figure 4a). Mean±SEM peak I_K1 densities evoked at -120 mV from a holding potential of -70 mV in wild-type and Kv4.2W362F-expressing myocytes were 11±0.5 pA/pF (n=19) and 12±0.5 pA/pF (n=18), respectively (Figure 4a).

View larger version (21K): [in this window] [in a new window]   Figure 3. Functional consequences of Kv4.2W362F expression in transgenic mice. a to d, Whole-cell outward K+ currents, recorded from ventricular myocytes isolated from adult nontransgenic (a and c) and transgenic (b and d) littermates, were evoked during 200-ms (a and b) or 3-s (c and d) depolarizing voltage steps to potentials between -50 and +60 mV from a holding potential of -70 mV. The waveforms of the Ca2+-independent depolarization-activated outward K+ currents in wild-type (a and c) and transgenic (b and d) myocytes are distinct: the amplitudes and the rates of decay of the peak outward K+ currents recorded from ventricular myocytes isolated from Kv4.2W362F-expressing animals (b and d) are reduced compared with those (a and c) recorded from nontransgenic, ie, wild-type, cells. To examine the decay phases of the outward K+ currents, the same voltage-clamp protocol as used in panels a and b was used in panels c and d except that the voltage-step durations were increased from 200 ms to 3 s. e and f, Current-clamp recordings reveal marked action potential prolongation in Kv4.2W362F-expressing ventricular myocytes (f) compared with ventricular myocytes isolated from nontransgenic littermates (e). Scale bars are 2 nA and 20 ms in panels a and b, 2 nA and 200 ms in panels c and d, and 40 mV and 40 ms in panels e and f.

View larger version (12K): [in this window] [in a new window]   Figure 4. The densities and the decay rates of the peak outward K+ currents are altered in ventricular myocytes expressing Kv4.2W362F. a, Mean±SEM K+ current densities in nontransgenic and Kv4.2W362F-expressing ventricular myocytes are illustrated. Peak and plateau outward K+ currents, evoked at +20 mV from a holding potential of -70 mV, were measured in individual cells (see Materials and Methods) and normalized to the whole-cell membrane capacitance (determined in the same cell); mean±SEM peak (n=40) and plateau (n=18) densities are plotted. The amplitudes of inwardly rectifying K+ currents (IK1), evoked on membrane hyperpolarization to –120 mV from a holding potential of -70 mV, were measured in individual cells and normalized to the whole-cell membrane capacitance (determined in the same cell); mean±SEM IK1 densities (n=18) are plotted. Only peak outward K+ current density is attenuated in Kv4.2W362F-expressing cells. b, Mean±SEM inactivation time constants ( values), obtained from double-exponential fits to the decay phases of the outward currents (see Materials and Methods), are plotted as a function of test potential. As is evident, the time constants of inactivation of both the fast and the slow components of peak outward current decay in ventricular myocytes isolated from wild-type and transgenic littermates are voltage independent. The time constants of inactivation for the fast component of peak outward current decay, however, are significantly different at all test potentials, whereas there are no significant differences in the time constants of inactivation of the slow component of peak outward decay when the values obtained in nontransgenic and Kv4.2W362F-expressing myocytes are compared (see text).

Action Potentials and QT Intervals Are Prolonged in Kv4.2W362F-Expressing Animals
In current-clamp experiments, action potentials recorded from Kv4.2W362F-expressing isolated ventricular myocytes (Figure 3f) are substantially broader than action potentials recorded from cells isolated from nontransgenic littermates (Figure 3e), consistent with the elimination of I_to. Analysis of action potential durations at 90% repolarization revealed mean±SEM values of 36±10 ms (n=9) and 116±14 ms (n=9) in wild-type and Kv4.2W362F-expressing cells, respectively; these values are significantly (at the P<0.001 level) different. In contrast, action potential amplitudes and resting membrane potentials of the Kv4.2W362F-expressing myocytes are not significantly different from those measured in wild-type cells.

To determine the functional consequences of the marked prolongation of ventricular action potentials, surface ECGs were recorded from Kv4.2W362F-expressing transgenic and nontransgenic littermates (Figure 5). Analysis of the ECGs revealed a marked prolongation of the QT interval in the transgenic animals, consistent with the underlying defect being in ventricular repolarization. Mean±SEM QT intervals in wild-type and transgenic animals were found to equal 79±5 ms (n=5) and 121±5 ms (n=12), respectively; these values are significantly different at the P<0.001 level. Neither heart rates (RR intervals) nor QRS durations, however, were affected by Kv4.2W362F expression. Mean±SEM RR intervals were 193±19 ms (n=5) and 250±23 ms (n=12) in wild-type and Kv4.2W362F-expressing animals, respectively, and mean±SEM QRS durations were 10.8±0.4 ms (n=5) and 11.2±0.2 ms (n=12) in control and transgenic animals, respectively. When QT intervals were corrected for heart rate,²⁸ the differences between the transgenic and the nontransgenic animals were also highly significant (at the P<0.001 level): mean±SEM QTc intervals (see Materials and Methods) were 57±3 ms (n=5) and 79±3 ms (n=12) in control and Kv4.2W262-expressing animals, respectively.

View larger version (17K): [in this window] [in a new window]   Figure 5. Prolongation of the QT interval is evident in ECG recordings from Kv4.2W362F-expressing mice. ECGs were recorded as described in Materials and Methods with electrode position optimized to permit reliable resolution of the T waves and accurate measurements of the QT intervals. P waves and QRS and QT intervals are clearly labeled in the records obtained from the nontransgenic (a) and Kv4.2W362F-expressing (b) mice; the scale bar is 100 ms.

Upregulation of a Novel Current in Kv4.2W362F-Expressing Ventricular Myocytes
As is evident in Figure 3, the waveforms of the depolarization-activated K⁺ currents in ventricular myocytes isolated from wild-type and Kv4.2W362F-expressing littermates are distinct. Specifically, the fast component of inactivation (attributed to I_to³⁰) appears to be markedly reduced or eliminated in the Kv4.2W362F-expressing cells (Figure 3b and 3d). Analysis of the decay phases of the currents evoked during 3-s voltage steps confirmed this impression. For wild-type myocytes, the decay phases of the peak outward currents were well described by the sum of 2 exponentials with mean±SEM time constants of 72±4 ms (n=18) and 956±45 ms (n=18); these values are similar to those recently reported by Wang and Duff³⁰ (1997) and London et al²⁸ (1998). As also reported previously,³⁰ neither the fast nor the slow component of peak outward current decay in wild-type cells displays any appreciable voltage dependence (Figure 4b). The decay phases of the currents in Kv4.2W362F-expressing myocytes were also well described by the sum of 2 exponentials. In this case, however, the mean±SEM decay time constants were 212±19 ms (n=13) and 1140±85 ms (n=13), and similar to the findings in wild-type cells, neither time constant varies with voltage (Figure 4b). Importantly, the very rapid component of current decay in wild-type mouse ventricular myocytes (_decay, 70 ms), which reflects I_to,^{28 30} is not evident in the transgenic cells (Figure 3b and 3d), consistent with the "functional knockout" of I_to. Similar results have been obtained in voltage-clamp experiments completed on ventricular myocytes isolated from progeny of transgenic founders 15 and 27; ie, I_to is also functionally eliminated in these cells. The mean±SEM time constants of inactivation of the slower components of current decay are not significantly different, suggesting that the slow components of current decay in wild-type (_decay, 956±45 ms) and Kv4.2W362F-expressing (_decay, 1145±85 ms) ventricular myocytes are the same. Interestingly, this slowly inactivating K⁺ current is selectively attenuated in transgenic mice²⁸ expressing a dominant-negative Kv1.1 construct, Kv1.1N206Tag.³¹

Inactivation of the fast component of peak outward current decay (mean±SEM _decay, 212±19 ms) in Kv4.2W362F-expressing ventricular myocytes is significantly (P0.001) slower than I_to (_decay, 70 ms) at all test potentials (Figure 4b). Because the experiments on QT-6 cells (Figure 1) revealed that coexpression of the Kv4.2W362F with wild-type Kv4 subunits reduces K⁺ current amplitudes/densities without changing the kinetic properties of the currents, it seems unlikely that the fast component of current decay in Kv4.2W362F-expressing ventricular myocytes reflects (modified) I_to. Rather, the results suggest that in the absence of I_to, a "novel" inactivating current component is revealed, ie, a current that is not evident in wild-type cells. It might also be suggested, however, that eliminating the majority of I_to channels reveals a current that is not apparent in wild-type cells, simply because the density of this current is too low relative to I_to to be resolved. The fact that the time constants for inactivation of I_to (_decay, 70 ms) and the novel current (_decay, 200 ms) differ by less than a factor of 3 would further complicate resolution of the 2 current components. To test the hypothesis that the novel current might also be present in wild-type cells, the decay phases of the currents were fitted by the sum of 3 exponentials with fixed time constants of 70 ms (for I_to), 200 ms (for the novel transgenic current), and 1 s (for the slowly inactivating current).

As might be expected, these analyses revealed that the decay phases of the currents could indeed be fitted by the sum of 3 exponentials, and the mean±SEM (n=10) densities of the current components at +20 mV were as follows: 20.1±3.8 pA/pF for I_to, 3.1±0.9 for the current with the _decay of 200 ms, and 15.8±1.3 pA/pF for the slowly decaying K⁺ current. The density of the novel current (_decay, 200 ms) predicted by this analysis, therefore, is very low. In addition, the fits suggest that this current component contributes 7±2% to the peak outward current, whereas the I_to and the slowly decaying currents contribute 44±4% and 34±3%, respectively, to the peak current; 15% of the peak outward K⁺ current is noninactivating (Figure 3c). In Kv4.2W362F-expressing ventricular myocytes, however, the novel current contributes 50% to the peak outward current, with a mean±SEM density of 8.3±0.6 pA/pF (n=10). Thus, even if expressed in wild-type myocytes, the results demonstrate that the novel current is markedly upregulated in Kv4.2W362F-expressing myocytes. More important, however, is the fact that the quality of the fits to the decay phases of the currents in wild-type cells was not improved by the inclusion of the third component (_decay, 200 ms). We suggest, therefore, that there are 2 (not 3) inactivating components of the outward K⁺ currents in wild-type myocytes, I_to (mean±SEM _decay, 72±4 ms) and the slowly decaying current (mean±SEM _decay, 956±45 ms), and we further suggest that the current in the transgenic cells with the mean±SEM _decay of 212±19 ms reflects a novel current that is not expressed in wild-type cells (see Discussion).

	Discussion

Top Abstract Introduction Materials and Methods Results Discussion References

 
Functional Consequences of Cardiac-Specific Expression of Kv4.2W362F
The results presented here reveal that I_to is functionally eliminated in myocytes isolated from Kv4.2W362F-expressing animals, demonstrating directly that members of the Kv4 -subunit subfamily underlie I_to in the mouse ventricle. The functional knockout of I_to results in increased action potential durations in single ventricular myocytes and prolongation of the QT interval recorded in surface ECGs. Therefore, it would seem reasonable to suggest that the Kv4.2W362F transgenics could potentially provide a rational experimental model for probing the molecular mechanisms underlying long-QT syndromes and other cardiac arrhythmias. Interestingly, however, in spite of the marked increases in action potential durations and QT intervals, the expression of Kv4.2W362F does not appear to have profound physiological or pathophysiological consequences. In fact, the Kv4.2W362F-expressing animals appear normal in every respect, and in experiments completed to date, we find no evidence that these animals are prone to develop arrhythmias. However, experiments aimed at determining if there are experimental conditions (such as pacing and adrenergic stimulation) that result in sustained arrhythmias in Kv4.2W362F-expressing animals/hearts are certainly warranted.

Recently, London et al²⁸ reported the generation and characterization of long-QT mice expressing a truncated Kv1.1 subunit (Kv1.1N206Tag)³¹ that also functions as a dominant negative. Expression of the Kv1.1N206Tag selectively attenuates the slowly decaying component of the total depolarization-activated K⁺ current in mouse ventricular myocytes, consistent with the hypothesis that a member of the Kv1 subfamily, likely Kv1.5, underlies this (slowly inactivating) K⁺ current.^{28 32} Similar to the results presented here, cardiac-specific expression of Kv1.1N206Tag results in prolonged ventricular action potentials and QT intervals.²⁸ Interestingly, however, and in contrast to the results reported in the present study, London et al²⁸ also reported increased frequency of premature ventricular beats, ventricular arrhythmias, and spontaneous ventricular tachyarrhythmias in Kv1.1N206Tag-expressing mice. As noted above, however, the Kv4.2W362F-expressing animals do not have spontaneous ventricular arrhythmias. In addition, it is of interest to note that the increases in action potential durations observed in Kv4.2W362F-expressing ventricular myocytes and the QT prolongation in Kv4.2W362F-expressing animals are both larger those seen in the Kv1.1N206Tag-expressing transgenics.²⁸ Taken together, these results suggest that factors in addition to prolonged ventricular repolarization play an important role in determining the propensity to develop and to sustain arrhythmias. Clearly, studies focused on exploring the molecular mechanisms underlying the markedly different phenotypes of Kv4.2W362F- and Kv1.1N206Tag-expressing mice are warranted.

Upregulation of a Novel Current in Kv4.2W362F-Expressing Ventricular Myocytes
In addition to providing a direct link between I_to and the Kv4 subfamily of subunits, the results of the present study demonstrate that a novel, rapidly activating, slowly inactivating current component is revealed when functional I_to channels are eliminated. This intriguing finding suggests that the downregulation of one channel type, in this case I_to, influences the expression of other channel types, and preliminary experiments suggest that the upregulation of a Kv subunit that is not abundant in wild-type animals underlies this novel K⁺ conductance pathway. Interestingly, previous studies have demonstrated that Kv -subunit message levels can change in response to a number of physiological stimuli, including cAMP,³³ depolarization,³³ dexamethasone,³⁴ and stress,³⁴ suggesting that Kv -subunit expression in the heart might be highly regulated. With the use of the Kv4.2W362F-expressing transgenic mice, it will now be possible to begin to explore the molecular mechanism(s) underlying functional electrical remodeling of the heart and to determine whether remodeling is dependent on changes in the expression of specific ion channels (I_to) and/or specific alterations in cardiac electrical activity. Ongoing experiments are aimed at determining the detailed time- and voltage-dependent properties, as well as the pharmacological sensitivity, of the current that is upregulated in the Kv4.2W362F-expressing animals. Experiments focused on identifying the Kv subunit(s) that underlies the novel K⁺ current that is upregulated in Kv4.2W362F-expressing animals have also been initiated.

	Acknowledgments

 
Financial support provided by the National Heart, Lung, and Blood Institute of the National Institutes of Health and the Washington University/Monsanto/Searle Biomedical Research Agreement is gratefully acknowledged. We thank Mia Nichol, Andrew Benedict, and Bridget Scheve for technical assistance in the generation, screening, and maintenance of the transgenic mice. We also thank Drs Josh Sanes and Colin Nichols for many helpful comments and discussions throughout the course of this work. Finally, we thank Dr Jeffery Robbins (University of Cincinnati) for the -MHC transgenic construct, Drs Jane Dixon and David McKinnon (State University of New York at Stony Brook) for providing us with the Kv4.3 cDNA, and Drs Morgan Sheng (Harvard University) and Lily Y. Jan (University of California at San Francisco) for the Kv4.2 cDNA.

Received April 20, 1998; accepted July 17, 1998.

	References

Top Abstract Introduction Materials and Methods Results Discussion References

 
1. Barry DM, Nerbonne JM. Myocardial potassium channels: electrophysiological and molecular diversity. Annu Rev Physiol. 1996;58:363–394.[Medline] [Order article via Infotrieve]

2. Campbell DL, Rasmusson RL, Comer MB, Strauss HC. The cardiac calcium-independent transient outward potassium current: kinetics, molecular properties, and role in ventricular repolarization. In: Zipes DP, Jalife J, eds. Cardiac Electrophysiology: From Cell to Bedside. 2nd ed. Philadelphia, Pa: WB Saunders Co; 1995:83–96.

3. Kass RS. Delayed potassium channels in the heart: cellular, molecular, and regulatory properties In: Zipes DP, Jalife J, eds. Cardiac Electrophysiology: From Cell to Bedside. 2nd ed. Philadelphia, Pa: WB Saunders Co; 1995:74–82.

4. Potreau D, Gomez JP, Fares N. Depressed transient outward current in single hypertrophied cardiomyocytes isolated from the right ventricle of ferret heart. Cardiovasc Res. 1995;30:440–448.[Medline] [Order article via Infotrieve]

5. Gidh-Jain M, Huang B, Jain P, El-Sherif N. Differential expression of voltage-gated K⁺ channel genes in left ventricular remodeled myocardium after experimental myocardial infarction. Circ Res. 1996;79:669–675.[Abstract/Free Full Text]

6. Van Wagoner DR, Pond AL, McCarthy PM, Trimmer JS, Nerbonne JM. Outward K⁺ current densities and Kv1.5 expression are reduced in chronic human atrial fibrillation. Circ Res. 1997;80:772–781.[Abstract/Free Full Text]

7. Wang Q, Curran ME, Splawski I, Burn TC, Millholland JM, VanRay TJ, Shen J, Timothy KW, Vincent GM, deJager T, Schwartz PJ, Toubin JA, Moss AJ, Atkinson DL, Landes GM, Connors TD, Keating MT. Positional cloning of a novel potassium channel gene: KvLQT1 mutations cause cardiac arrhythmias. Nat Genet. 1996;12:17–23.[Medline] [Order article via Infotrieve]

8. Curran ME, Splawski I, Timothy KW, Vincent GM, Green ED, Keating MT. A molecular basis for cardiac arrhythmia: herg mutations cause long QT syndrome. Cell. 1995;80:795–803.[Medline] [Order article via Infotrieve]

9. Sanguinetti MC, Jiang C, Curran ME, Keating MT. A mechanistic link between an inherited and an acquired cardiac arrhythmia: HERG encodes the I_Kr potassium channel. Cell. 1995;81:299–307.[Medline] [Order article via Infotrieve]

10. Trudeau MC, Warmke JW, Ganetzky B, Robertson, GA. HERG, a human inward rectifier in the voltage-gated potassium channel family. Science. 1995;269:92–95.[Abstract/Free Full Text]

11. Barhanin J, Lesage F, Guillemare E, Fink M, Lazdunski M, Romey G. KvLQT1 and IsK (minK) proteins associate to form the I_Ks cardiac potassium current. Nature. 1996;384:78–80.[Medline] [Order article via Infotrieve]

12. Sanguinetti MC, Curran ME, Zou A, Shen J, Spector PS, Atkinson DL, Keating MT. Coassembly of KvLQT1 and minK (IsK) proteins to form cardiac I_Ks potassium channel. Nature. 1996;384:80–83.[Medline] [Order article via Infotrieve]

13. Dixon JE, McKinnon D. Quantitative analysis of potassium channel mRNA expression in atrial and ventricular muscle of rats. Circ Res. 1994;75:252–260.[Abstract/Free Full Text]

14. Barry DM, Trimmer JS, Merlie JP, Nerbonne JM. Differential expression of voltage-gated K⁺ channel subunits in adult rat heart: relationship to functional K⁺ channels? Circ Res. 1995;77:361–369.[Abstract/Free Full Text]

15. Dixon JE, Shi W, Wang H-S, McDonald C, Yu H, Wymore RS, Cohen IS, McKinnon D. Role of the Kv4.3 K⁺ channel in ventricular muscle: a molecular correlate for the transient outward current. Circ Res. 1996;79:659–668.[Abstract/Free Full Text]

16. Xu H, Dixon JE, Barry DM, Trimmer JS, Merlie JP, McKinnon D, Nerbonne JM. Developmental analysis reveals mismatches in the expression of K⁺ channel subunits and voltage-gated K⁺ channel currents in rat ventricular myocytes. J Gen Physiol. 1996;108:405–419.[Abstract/Free Full Text]

17. Fiset C, Clark RB, Shimoni Y, Giles WR. Shal-type channels contribute to the Ca²⁺-independent transient outward K⁺ current in rat ventricle. J Physiol (Lond). 1997;500:51–64.[Abstract/Free Full Text]

18. Sanguinetti MC, Johnson JH, Hammerland LG, Kelbaugh PR, Volkmann RA, Saccomano NA, Mueller AL. Heteropodatoxins: peptides isolated from spider venom that block Kv4.2 potassium channels. Mol Pharmacol. 1997;51:491–498.[Abstract/Free Full Text]

19. Po S, Roberds S, Snyders DJ, Tamkun MM, Bennett PB. Heteromultimeric assembly of human potassium channels: molecular basis of a transient outward current? Circ Res. 1993;72:1326–1336.[Abstract/Free Full Text]

20. Murray KT, Fahrig SA, Deal KK, Po SS, Hu NN, Snyders DJ, Tamkun MM, Bennett PB. Modulation of an inactivating human cardiac K⁺ channel by protein kinase C. Circ Res. 1994;75:999–1005.[Abstract/Free Full Text]

21. Perozo E, MacKinnon R, Benzanilla F, Stefani E. Gating currents from a nonconducting mutant reveal open-closed conformations in Shaker K⁺ channels. Neuron. 1993;11:353–358.[Medline] [Order article via Infotrieve]

22. Ribera AB. Homogeneous development of electrical excitability via heterogeneous ion channel expression. J Neurosci. 1996;16:1123–1130.[Abstract/Free Full Text]

23. Lyons GE, Schiaffino S, Sasson D, Barton P, Buckingham M. Developmental regulation of myosin gene expression in mouse cardiac muscle. J Cell Biol. 1990;111:2427–2436.[Abstract/Free Full Text]

24. Ng WA, Grupp IL, Subramaniam A, Robbins J. Cardiac myosin heavy chain mRNA expression and myocardial function in the mouse heart. Circ Res. 1991;68:1742–1750.[Abstract/Free Full Text]

25. Koch WJ, Rockman HA, Samama P, Hamilton RA, Bond RA, Milano CA, Lefkowitz RJ. Cardiac function in mice overexpressing the ß-adrenergic receptor kinase or a ßARK inhibitor. Science. 1995;268:1350–1352.[Abstract/Free Full Text]

26. Palermo J, Gulick J, Colbert M, Fewell J, Robbins J. Transgenic remodeling of the contractile apparatus in the mammalian heart. Circ Res. 1996;78:504–509.[Abstract/Free Full Text]

27. Guerrero PA, Schuessler RB, Davis LM, Beyer EC, Johnson CM, Yamada KA, Saffitz JE. Slow ventricular conduction in mice heterozygous for a connexin 43 null mutation. J Clin Invest. 1997;99:1991–1998.[Medline] [Order article via Infotrieve]

28. London B, Jeron A, Zhou J, Buckett P, Han X, Mitchell GF, Koren G. Long QT and ventricular arrhythmias in transgenic mice expressing the N terminus and first transmembrane segment of a voltage-gated potassium channel. Proc Natl Acad Sci U S A. 1998;95:2926–2931.[Abstract/Free Full Text]

29. Covarrubias M, Wei A, Salkoff L. Shaker, Shal, Shab, and Shaw express independent K⁺ current systems. Neuron. 1991;7:763–773.[Medline] [Order article via Infotrieve]

30. Wang L, Duff HJ. Developmental changes in transient outward current in mouse ventricle. Circ Res. 1997;81:120–127.[Abstract/Free Full Text]

31. Folco E, Mathur R, Mori Y, Buckett P, Koren G. A cellular model for long QT syndrome: trapping of heteromultimeric complexes consisting of truncated Kv1.1 potassium channel polypeptides and native Kv1.4 and Kv1.5 channels in the endoplasmic reticulum. J Biol Chem. 1997;272:26505–26510.[Abstract/Free Full Text]

32. Fiset C, Clark RB, Larsen TS, Giles WR. A rapidly activating, sustained current modulates repolarization and excitation-contraction coupling in adult mouse ventricle. J Physiol (Lond). 1997;504:557–563.[Abstract/Free Full Text]

33. Mori Y, Matsubara H, Folco E, Siegal A, Koren G. The transcription of a mammalian voltage-gated potassium channel is regulated by cAMP in a cell-specific manner. J Biol Chem.. 1993;268:26482–26493.[Abstract/Free Full Text]

34. Levitan ES, Hershman KM, Sherman TG, Takimoto K. Dexamethasone and stress upregulate Kv1.5 K⁺ channel gene expression in rat ventricular myocytes. Neuropharmacology. 1996;35:1001–1006.[Medline] [Order article via Infotrieve]

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				X.-G. Lai, J. Yang, S.-S. Zhou, J. Zhu, G.-R. Li, and T.-M. Wong Involvement of anion channel(s) in the modulation of the transient outward K+ channel in rat ventricular myocytes Am J Physiol Cell Physiol, July 1, 2004; 287(1): C163 - C170. [Abstract] [Full Text] [PDF]

				B. Rosati and D. McKinnon Regulation of Ion Channel Expression Circ. Res., April 16, 2004; 94(7): 874 - 883. [Abstract] [Full Text] [PDF]

				G. Liu, J. B. Iden, K. Kovithavongs, R. Gulamhusein, H. J. Duff, and K. M. Kavanagh In vivo temporal and spatial distribution of depolarization and repolarization and the illusive murine T wave J. Physiol., February 15, 2004; 555(1): 267 - 279. [Abstract] [Full Text] [PDF]

				S. A. Kodirov, M. Brunner, J. M. Nerbonne, P. Buckett, G. F. Mitchell, and G. Koren Attenuation of IK,slow1 and IK,slow2 in Kv1/Kv2DN mice prolongs APD and QT intervals but does not suppress spontaneous or inducible arrhythmias Am J Physiol Heart Circ Physiol, January 1, 2004; 286(1): H368 - H374. [Abstract] [Full Text] [PDF]

				H. Li, W. Guo, K. A. Yamada, and J. M. Nerbonne Selective elimination of IK,slow1 in mouse ventricular myocytes expressing a dominant negative Kv1.5{alpha} subunit Am J Physiol Heart Circ Physiol, January 1, 2004; 286(1): H319 - H328. [Abstract] [Full Text] [PDF]

				W. Dun, P. Chandra, P. Danilo Jr., M. R. Rosen, and P. A. Boyden Chronic atrial fibrillation does not further decrease outward currents. It increases them. Am J Physiol Heart Circ Physiol, October 1, 2003; 285(4): H1378 - H1384. [Abstract] [Full Text] [PDF]

				R. Shibata, H. Misonou, C. R. Campomanes, A. E. Anderson, L. A. Schrader, L. C. Doliveira, K. I. Carroll, J. D. Sweatt, K. J. Rhodes, and J. S. Trimmer A Fundamental Role for KChIPs in Determining the Molecular Properties and Trafficking of Kv4.2 Potassium Channels J. Biol. Chem., September 19, 2003; 278(38): 36445 - 36454. [Abstract] [Full Text] [PDF]

				I. Bodi, J. N. Muth, H. S. Hahn, N. N. Petrashevskaya, M. Rubio, S. E. Koch, G. Varadi, and A. Schwartz Electrical remodeling in hearts from a calcium-dependent mouse model of hypertrophy and failure: Complex nature of k+ current changes and action potential duration J. Am. Coll. Cardiol., May 7, 2003; 41(9): 1611 - 1622. [Abstract] [Full Text] [PDF]

				G. C. Amberg, S. D. Koh, Y. Imaizumi, S. Ohya, and K. M. Sanders A-type potassium currents in smooth muscle Am J Physiol Cell Physiol, March 1, 2003; 284(3): C583 - C595. [Abstract] [Full Text] [PDF]

				S. L. Bouter, S. Demolombe, A. Chambellan, C. Bellocq, F. Aimond, G. Toumaniantz, G. Lande, S. Siavoshian, I. Baro, A. L. Pond, et al. Microarray Analysis Reveals Complex Remodeling of Cardiac Ion Channel Expression With Altered Thyroid Status: Relation to Cellular and Integrated Electrophysiology Circ. Res., February 7, 2003; 92(2): 234 - 242. [Abstract] [Full Text] [PDF]

				J. Zhou, S. Kodirov, M. Murata, P. D. Buckett, J. M. Nerbonne, and G. Koren Regional upregulation of Kv2.1-encoded current, IK,slow2, in Kv1DN mice is abolished by crossbreeding with Kv2DN mice Am J Physiol Heart Circ Physiol, February 1, 2003; 284(2): H491 - H500. [Abstract] [Full Text] [PDF]

				D. Dong, Y. Duan, J. Guo, D. E Roach, S. L Swirp, L. Wang, J.P Lees-Miller, R.S Sheldon, J. D Molkentin, and H. J Duff Overexpression of calcineurin in mouse causes sudden cardiac death associated with decreased density of K+ channels Cardiovasc Res, February 1, 2003; 57(2): 320 - 332. [Abstract] [Full Text] [PDF]

				J. Brouillette, V. Trepanier-Boulay, and C. Fiset Effect of androgen deficiency on mouse ventricular repolarization J. Physiol., January 15, 2003; 546(2): 403 - 413. [Abstract] [Full Text] [PDF]

				C. Chiello Tracy, C. Cabo, J. Coromilas, J. Kurokawa, R. S. Kass, and A. L. Wit Electrophysiological consequences of human IKs channel expression in adult murine heart Am J Physiol Heart Circ Physiol, January 1, 2003; 284(1): H168 - H175. [Abstract] [Full Text] [PDF]

				S. A. Malin and J. M. Nerbonne Delayed Rectifier K+ Currents, IK, Are Encoded by Kv2 alpha -Subunits and Regulate Tonic Firing in Mammalian Sympathetic Neurons J. Neurosci., December 1, 2002; 22(23): 10094 - 10105. [Abstract] [Full Text] [PDF]

				C. Zobel, Z. Kassiri, T.-T. T. Nguyen, Y. Meng, and P. H. Backx Prevention of Hypertrophy by Overexpression of Kv4.2 in Cultured Neonatal Cardiomyocytes Circulation, October 29, 2002; 106(18): 2385 - 2391. [Abstract] [Full Text] [PDF]

				T. Sacco and F. Tempia A-Type potassium currents active at subthreshold potentials in mouse cerebellar purkinje cells J. Physiol., September 1, 2002; 543(2): 505 - 520. [Abstract] [Full Text] [PDF]

				W. Guo, S. A. Malin, D. C. Johns, A. Jeromin, and J. M. Nerbonne Modulation of Kv4-encoded K+ Currents in the Mammalian Myocardium by Neuronal Calcium Sensor-1 J. Biol. Chem., July 12, 2002; 277(29): 26436 - 26443. [Abstract] [Full Text] [PDF]

				P. Escoubas, S. Diochot, M.-L. Celerier, T. Nakajima, and M. Lazdunski Novel Tarantula Toxins for Subtypes of Voltage-Dependent Potassium Channels in the Kv2 and Kv4 Subfamilies Mol. Pharmacol., July 1, 2002; 62(1): 48 - 57. [Abstract] [Full Text] [PDF]

				S. Danik, C. Cabo, C. Chiello, S. Kang, A. L. Wit, and J. Coromilas Correlation of repolarization of ventricular monophasic action potential with ECG in the murine heart Am J Physiol Heart Circ Physiol, July 1, 2002; 283(1): H372 - H381. [Abstract] [Full Text] [PDF]

				K. B Walsh and G. E Parks Changes in cardiac myocyte morphology alter the properties of voltage-gated ion channels Cardiovasc Res, July 1, 2002; 55(1): 64 - 75. [Abstract] [Full Text] [PDF]

				M. A Lazaroff, A. D Taylor, and A. B Ribera In vivo analysis of Kv{beta}2 function in Xenopus embryonic myocytes J. Physiol., June 15, 2002; 541(3): 673 - 683. [Abstract] [Full Text] [PDF]

				N. N Petrashevskaya, I. Bodi, M. Rubio, J. D Molkentin, and A. Schwartz Cardiac function and electrical remodeling of the calcineurin-overexpressed transgenic mouse Cardiovasc Res, April 1, 2002; 54(1): 117 - 132. [Abstract] [Full Text] [PDF]

				M. C. Sanguinetti Reduced Transient Outward K+ Current and Cardiac Hypertrophy: Causal Relationship or Epiphenomenon? Circ. Res., March 22, 2002; 90(5): 497 - 499. [Full Text] [PDF]

				Z. Kassiri, C. Zobel, T.-T. T. Nguyen, J. D. Molkentin, and P. H. Backx Reduction of Ito Causes Hypertrophy in Neonatal Rat Ventricular Myocytes Circ. Res., March 22, 2002; 90(5): 578 - 585. [Abstract] [Full Text] [PDF]

				W. Guo, H. Li, F. Aimond, D. C. Johns, K. J. Rhodes, J. S. Trimmer, and J. M. Nerbonne Role of Heteromultimers in the Generation of Myocardial Transient Outward K+ Currents Circ. Res., March 22, 2002; 90(5): 586 - 593. [Abstract] [Full Text] [PDF]

				Y. Wu and M. E Anderson Reduced repolarization reserve in ventricular myocytes from female mice Cardiovasc Res, February 15, 2002; 53(3): 763 - 769. [Abstract] [Full Text] [PDF]

				M. H. Holmqvist, J. Cao, R. Hernandez-Pineda, M. D. Jacobson, K. I. Carroll, M. A. Sung, M. Betty, P. Ge, K. J. Gilbride, M. E. Brown, et al. Elimination of fast inactivation in Kv4 A-type potassium channels by an auxiliary subunit domain PNAS, January 22, 2002; 99(2): 1035 - 1040. [Abstract] [Full Text] [PDF]

				M. S Nadal, Y. Amarillo, E. V.-S. de Miera, and B. Rudy Evidence for the presence of a novel Kv4-mediated A-type K+ channel-modifying factor J. Physiol., December 15, 2001; 537(3): 801 - 809. [Abstract] [Full Text] [PDF]

				Members of the Sicilian Gambit New Approaches to Antiarrhythmic Therapy, Part I: Emerging Therapeutic Applications of the Cell Biology of Cardiac Arrhythmias Circulation, December 4, 2001; 104(23): 2865 - 2873. [Abstract] [Full Text] [PDF]

				Members of the Sicilian Gambit New approaches to antiarrhythmic therapy; emerging therapeutic applications of the cell biology of cardiac arrhythmias Eur. Heart J., December 1, 2001; 22(23): 2148 - 2163. [Abstract] [PDF]

				Members of the Sicilian Gambit New approaches to antiarrhythmic therapy: emerging therapeutic applications of the cell biology of cardiac arrhythmias Cardiovasc Res, December 1, 2001; 52(3): 345 - 360. [Abstract] [Full Text] [PDF]

				J. M. Nerbonne, C. G. Nichols, T. L. Schwarz, and D. Escande Genetic Manipulation of Cardiac K+ Channel Function in Mice: What Have We Learned, and Where Do We Go From Here? Circ. Res., November 23, 2001; 89(11): 944 - 956. [Abstract] [Full Text] [PDF]

				H. Li, W. Guo, H. Xu, R. Hood, A. T. Benedict, and J. M. Nerbonne Functional expression of a GFP-tagged Kv1.5 alpha -subunit in mouse ventricle Am J Physiol Heart Circ Physiol, November 1, 2001; 281(5): H1955 - H1967. [Abstract] [Full Text] [PDF]

				N. Decher, O. Uyguner, C. R Scherer, B. Karaman, M. Yuksel-Apak, A. E Busch, K. Steinmeyer, and B. Wollnik hKChIP2 is a functional modifier of hKv4.3 potassium channels: Cloning and expression of a short hKChIP2 splice variant Cardiovasc Res, November 1, 2001; 52(2): 255 - 264. [Abstract] [Full Text] [PDF]

				S. A. Malin and J. M. Nerbonne Molecular Heterogeneity of the Voltage-Gated Fast Transient Outward K+ Current, IAf, in Mammalian Neurons J. Neurosci., October 15, 2001; 21(20): 8004 - 8014. [Abstract] [Full Text] [PDF]

				Z. Wang, W. Kutschke, K. E. Richardson, M. Karimi, and J. A. Hill Electrical Remodeling in Pressure-Overload Cardiac Hypertrophy: Role of Calcineurin Circulation, October 2, 2001; 104(14): 1657 - 1663. [Abstract] [Full Text] [PDF]

				M. Brunner, W. Guo, G. F. Mitchell, P. D. Buckett, J. M. Nerbonne, and G. Koren Characterization of mice with a combined suppression of Ito and IK,slow Am J Physiol Heart Circ Physiol, September 1, 2001; 281(3): H1201 - H1209. [Abstract] [Full Text] [PDF]

				I. Cavero and W. Crumb Native and cloned ion channels from human heart: laboratory models for evaluating the cardiac safety of new drugs Eur. Heart J. Suppl., September 1, 2001; 3(suppl_K): K53 - K63. [Abstract] [PDF]

				M. J. Hernandez-Benito, R. Macianskiene, K. R. Sipido, W. Flameng, and K. Mubagwa Suppression of Transient Outward Potassium Currents in Mouse Ventricular Myocytes by Imidazole Antimycotics and by Glybenclamide J. Pharmacol. Exp. Ther., August 1, 2001; 298(2): 598 - 606. [Abstract] [Full Text] [PDF]

				C. A. Ufret-Vincenty, D. J. Baro, and L. F. Santana Differential contribution of sialic acid to the function of repolarizing K+ currents in ventricular myocytes Am J Physiol Cell Physiol, August 1, 2001; 281(2): C464 - C474. [Abstract] [Full Text] [PDF]

				M. H. Holmqvist, J. Cao, M. H. Knoppers, M. E. Jurman, P. S. Distefano, K. J. Rhodes, Y. Xie, and W. F. An Kinetic Modulation of Kv4-Mediated A-Current by Arachidonic Acid Is Dependent on Potassium Channel Interacting Proteins J. Neurosci., June 15, 2001; 21(12): 4154 - 4161. [Abstract] [Full Text] [PDF]

				J. J Zaritsky, J. B Redell, B. L Tempel, and T. L Schwarz The consequences of disrupting cardiac inwardly rectifying K+ current (IK1) as revealed by the targeted deletion of the murine Kir2.1 and Kir2.2 genes J. Physiol., June 15, 2001; 533(3): 697 - 710. [Abstract] [Full Text] [PDF]

				R. A Li, J. Miake, U. C Hoppe, D. C Johns, E. Marban, and H B. Nuss Functional consequences of the arrhythmogenic G306R KvLQT1 K+ channel mutant probed by viral gene transfer in cardiomyocytes J. Physiol., May 15, 2001; 533(1): 127 - 133. [Abstract] [Full Text] [PDF]

				S. Demolombe, G. Lande, F. Charpentier, M. A van Roon, M. J.B van den Hoff, G. Toumaniantz, I. Baro, G. Guihard, N. Le Berre, A. Corbier, et al. Transgenic mice overexpressing human KvLQT1 dominant-negative isoform Part I: Phenotypic characterisation Cardiovasc Res, May 1, 2001; 50(2): 314 - 327. [Abstract] [Full Text] [PDF]

				G. Lande, S. Demolombe, A. Bammert, A. Moorman, F. Charpentier, and D. Escande Transgenic mice overexpressing human KvLQT1 dominant-negative isoform Part II: Pharmacological profile Cardiovasc Res, May 1, 2001; 50(2): 328 - 334. [Abstract] [Full Text] [PDF]

				U. C. Hoppe, E. Marban, and D. C. Johns Distinct gene-specific mechanisms of arrhythmia revealed by cardiac gene transfer of two long QT disease genes, HERG and KCNE1 PNAS, April 24, 2001; 98(9): 5335 - 5340. [Abstract] [Full Text] [PDF]

				T.-T. Zhang, K. Takimoto, A. F. R. Stewart, C. Zhu, and E. S. Levitan Independent Regulation of Cardiac Kv4.3 Potassium Channel Expression by Angiotensin II and Phenylephrine Circ. Res., March 16, 2001; 88(5): 476 - 482. [Abstract] [Full Text] [PDF]

				E. Bou-Abboud, H. Li, and J. M Nerbonne Molecular diversity of the repolarizing voltage-gated K+ currents in mouse atrial cells J. Physiol., December 1, 2000; 529(2): 345 - 358. [Abstract] [Full Text] [PDF]

				J. L. Greenstein, R. Wu, S. Po, G. F. Tomaselli, and R. L. Winslow Role of the Calcium-Independent Transient Outward Current Ito1 in Shaping Action Potential Morphology and Duration Circ. Res., November 24, 2000; 87(11): 1026 - 1033. [Abstract] [Full Text] [PDF]

				S. P. Thomas, L. Bircher-Lehmann, S. A. Thomas, J. Zhuang, J. E. Saffitz, and A. G. Kleber Synthetic Strands of Neonatal Mouse Cardiac Myocytes : Structural and Electrophysiological Properties Circ. Res., September 15, 2000; 87(6): 467 - 473. [Abstract] [Full Text] [PDF]

				A. W. Varga, A. E. Anderson, J. P. Adams, H. Vogel, and J. D. Sweatt Input-Specific Immunolocalization of Differentially Phosphorylated Kv4.2 in the Mouse Brain Learn. Mem., September 1, 2000; 7(5): 321 - 332. [Abstract] [Full Text]

				M. T. Perez-Garcia, J. R. Lopez-Lopez, A. M. Riesco, U. C. Hoppe, E. Marban, C. Gonzalez, and D. C. Johns Viral Gene Transfer of Dominant-Negative Kv4 Construct Suppresses an O2-Sensitive K+ Current in Chemoreceptor Cells J. Neurosci., August 1, 2000; 20(15): 5689 - 5695. [Abstract] [Full Text] [PDF]

				W. Han, Z. Wang, and S. Nattel A comparison of transient outward currents in canine cardiac Purkinje cells and ventricular myocytes Am J Physiol Heart Circ Physiol, August 1, 2000; 279(2): H466 - H474. [Abstract] [Full Text] [PDF]

				S. A. Malin and J. M. Nerbonne Elimination of the Fast Transient in Superior Cervical Ganglion Neurons with Expression of KV4.2W362F: Molecular Dissection of IA J. Neurosci., July 15, 2000; 20(14): 5191 - 5199. [Abstract] [Full Text] [PDF]

				T W Claydon, M R Boyett, A Sivaprasadarao, K Ishii, J M Owen, H A O'Beirne, R Leach, K Komukai, and C H Orchard Inhibition of the K+ channel Kv1.4 by acidosis: protonation of an extracellular histidine slows the recovery from N-type inactivation J. Physiol., July 15, 2000; 526(2): 253 - 264. [Abstract] [Full Text] [PDF]

				W. Guo, H. Li, B. London, and J. M. Nerbonne Functional Consequences of Elimination of Ito, f and Ito, s : Early Afterdepolarizations, Atrioventricular Block, and Ventricular Arrhythmias in Mice Lacking Kv1.4 and Expressing a Dominant-Negative Kv4 {alpha} Subunit Circ. Res., July 7, 2000; 87(1): 73 - 79. [Abstract] [Full Text] [PDF]

				J. M Nerbonne Molecular basis of functional voltage-gated K+ channel diversity in the mammalian myocardium J. Physiol., June 1, 2000; 525(2): 285 - 298. [Abstract] [Full Text] [PDF]

				B. C Knollmann, B. E C Knollmann-Ritschel, N. J Weissman, L. R Jones, and M. Morad Remodelling of ionic currents in hypertrophied and failing hearts of transgenic mice overexpressing calsequestrin J. Physiol., June 1, 2000; 525(2): 483 - 498. [Abstract] [Full Text] [PDF]

				A. Jeron, G. F. Mitchell, J. Zhou, M. Murata, B. London, P. Buckett, S. D. Wiviott, and G. Koren Inducible polymorphic ventricular tachyarrhythmias in a transgenic mouse model with a long Q-T phenotype Am J Physiol Heart Circ Physiol, June 1, 2000; 278(6): H1891 - H1898. [Abstract] [Full Text] [PDF]

				J. James, A. Sanbe, K. Yager, L. Martin, R. Klevitsky, and J. Robbins Genetic Manipulation of the Rabbit Heart via Transgenesis Circulation, April 11, 2000; 101(14): 1715 - 1721. [Abstract] [Full Text] [PDF]

				L. C. Baker, B. London, B.-R. Choi, G. Koren, and G. Salama Enhanced Dispersion of Repolarization and Refractoriness in Transgenic Mouse Hearts Promotes Reentrant Ventricular Tachycardia Circ. Res., March 3, 2000; 86(4): 396 - 407. [Abstract] [Full Text] [PDF]

				V. S. Chauhan, S. Tuvia, M. Buhusi, V. Bennett, and A. O. Grant Abnormal Cardiac Na+ Channel Properties and QT Heart Rate Adaptation in Neonatal AnkyrinB Knockout Mice Circ. Res., March 3, 2000; 86(4): 441 - 447. [Abstract] [Full Text] [PDF]

				W. H. DuBell, W. J. Lederer, and T. B. Rogers K+ currents responsible for repolarization in mouse ventricle and their modulation by FK-506 and rapamycin Am J Physiol Heart Circ Physiol, March 1, 2000; 278(3): H886 - H897. [Abstract] [Full Text] [PDF]

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