© 1999 American Heart Association, Inc.
UltraRapid Communication |
Ca2+ Influx Through Ca2+ Channels in Rabbit Ventricular Myocytes During Action Potential Clamp
Influence of Temperature
From the Department of Physiology (J.L.P., W.Y., D.M.B.), Loyola University Chicago, Maywood, Ill; Departamento de Engenharia Biomédica (J.L.P., J.W.M.B.), Universidade Estadual de Campinas, UNICAMP, Brazil.
Correspondence to Donald M. Bers, PhD, Department of Physiology, Loyola University Medical School, 2160 South First Ave, Maywood, IL 60153. E-mail dbers{at}luc.edu
Abstract—Ca2+ influx
via Ca2+ current (ICa) during
the action potential (AP) was determined at 25°C and 35°C in
isolated rabbit ventricular myocytes using AP clamp.
Contaminating currents through Na+ and K+
channels were eliminated by using Na+- and
K+-free solutions, respectively. DIDS (0.2 mmol/L) was
used to block Ca2+-activated chloride current
(ICl(Ca)). When the sarcoplasmic reticulum
(SR) was depleted of Ca2+ by preexposure to 10 mmol/L
caffeine, total Ca2+ entry via
ICa during the AP was 
12 µmol/L
cytosol (at both 25°C and 35°C). Similar Ca2+ influx at
35°C and 25°C resulted from a combination of higher and faster peak
ICa, offset by more rapid
ICa inactivation at 35°C. During repeated
AP clamps, the SR gradually fills with Ca2+, and consequent
SR Ca2+ release accelerates ICa
inactivation during the AP. During APs and contractions in steady
state, total Ca2+ influx via ICa
was reduced by 50% but was again unaltered by temperature
(5.6±0.2 µmol/L cytosol at 25°C, 6.0±0.2 µmol/L
cytosol at 35°C). Thus, SR Ca2+ release is responsible
for sufficient ICa inactivation to cut total
Ca2+ influx in half. However, because of the kinetic
differences in ICa, the amount of
Ca2+ influx during the first 10 ms, which presumably
triggers SR Ca2+ release, is much greater at 35°C.
ICa during a first pulse, given just after
the SR was emptied with caffeine, was subtracted from
ICa during each of 9 subsequent pulses,
which loaded the SR. These difference currents reflect
ICa inactivation due to SR Ca2+
release and thus indicate the time course of local [Ca2+]
in the subsarcolemmal space near Ca2+ channels produced by
SR Ca2+ release (eg, maximal at 20 ms after the AP
activation at 35°C). Furthermore, the rate of change of this
difference current may reflect the rate of SR Ca2+ release
as sensed by L-type Ca2+ channels. These results suggest
that peak SR Ca2+ release occurs within 2.5 or 5 ms of AP
upstroke at 35°C and 25°C, respectively.
ICl(Ca) might also indicate local
[Ca2+], and at 35°C in the absence of DIDS (when
ICl(Ca) is prominent), peak
ICl(Ca) also occurred at a time comparable
to the peak ICa difference current. We
conclude that SR Ca2+ release decreases the
Ca2+ influx during the AP by 50% (at both 25°C and
35°C) and that changes in ICa (and
ICl(Ca)), which depend on SR
Ca2+ release, provide information about local
subsarcolemmal [Ca2+]. The full text of this article is
available at http://www.circresaha.org.
Key Words: Ca2+ current • cardiac muscle • excitation-contraction coupling • sarcoplasmic reticulum Ca2+ release
This article has been cited by other articles:
 |
|
 |
|
  J. Altamirano and D. M. Bers Effect of intracellular Ca2+ and action potential duration on L-type Ca2+ channel inactivation and recovery from inactivation in rabbit cardiac myocytes Am J Physiol Heart Circ Physiol, July 1, 2007; 293(1): H563 - H573. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 G. M. Faber and Y. Rudy Calsequestrin mutation and catecholaminergic polymorphic ventricular tachycardia: A simulation study of cellular mechanism Cardiovasc Res, July 1, 2007; 75(1): 79 - 88. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 C. Pott, M. Yip, J. I. Goldhaber, and K. D. Philipson Regulation of Cardiac L-Type Ca2+ Current in Na+-Ca2+ Exchanger Knockout Mice: Functional Coupling of the Ca2+ Channel and the Na+-Ca2+ Exchanger Biophys. J., February 15, 2007; 92(4): 1431 - 1437. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 G. Antoons, P. G. A. Volders, T. Stankovicova, V. Bito, M. Stengl, M. A. Vos, and K. R. Sipido Window Ca2+ current and its modulation by Ca2+ release in hypertrophied cardiac myocytes from dogs with chronic atrioventricular block J. Physiol., February 15, 2007; 579(1): 147 - 160. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
F. Brette, L. Salle, and C. H. Orchard Quantification of Calcium Entry at the T-Tubules and Surface Membrane in Rat Ventricular Myocytes Biophys. J., January 1, 2006; 90(1): 381 - 389. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
T. R. Shannon, F. Wang, J. Puglisi, C. Weber, and D. M. Bers A Mathematical Treatment of Integrated Ca Dynamics within the Ventricular Myocyte Biophys. J., November 1, 2004; 87(5): 3351 - 3371. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. A. Bassani, J. Altamirano, J. L. Puglisi, and D. M. Bers Action potential duration determines sarcoplasmic reticulum Ca2+ reloading in mammalian ventricular myocytes J. Physiol., September 1, 2004; 559(2): 593 - 609. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 S. Vadakkadath Meethal, K. T. Potter, D. Redon, D. M. Heisey, and R. A. Haworth Ca transients from Ca channel activity in rat cardiac myocytes reveal dynamics of dyad cleft and troponin C Ca binding Am J Physiol Cell Physiol, February 1, 2004; 286(2): C302 - C316. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. Zahradnikova, Z. Kubalova, J. Pavelkova, S. Gyorke, and I. Zahradnik Activation of calcium release assessed by calcium release-induced inactivation of calcium current in rat cardiac myocytes Am J Physiol Cell Physiol, February 1, 2004; 286(2): C330 - C341. [Abstract] [Full Text]
|
|
|
|
|
|
Y. Shiferaw, M. A. Watanabe, A. Garfinkel, J. N. Weiss, and A. Karma Model of Intracellular Calcium Cycling in Ventricular Myocytes Biophys. J., December 1, 2003; 85(6): 3666 - 3686. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
C. I. Spencer and J. S. K. Sham Effects of Na+/Ca2+ exchange induced by SR Ca2+ release on action potentials and afterdepolarizations in guinea pig ventricular myocytes Am J Physiol Heart Circ Physiol, December 1, 2003; 285(6): H2552 - H2562. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. M Pogwizd, K. R Sipido, F. Verdonck, and D. M Bers Intracellular Na in animal models of hypertrophy and heart failure: contractile function and arrhythmogenesis Cardiovasc Res, March 15, 2003; 57(4): 887 - 896. [Full Text] [PDF]
|
|
|
|
|
|
J. L. Puglisi and D. M. Bers LabHEART: an interactive computer model of rabbit ventricular myocyte ion channels and Ca transport Am J Physiol Cell Physiol, December 1, 2001; 281(6): C2049 - C2060. [Abstract] [Full Text] [PDF]
|
|