Published online before print April 15, 2004, doi: 10.1161/01.RES.0000128408.66946.67
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© 2004 American Heart Association, Inc.
Cellular Biology |
Unique Kir2.x Properties Determine Regional and Species Differences in the Cardiac Inward Rectifier K+ Current
From the Department of Pharmacology and Institute for Cardiovascular Research, State University of New York Upstate Medical University, Syracuse.
Correspondence to Justus M.B. Anumonwo, PhD, Department of Pharmacology, State University of New York Upstate Medical University, 766 Irving Ave, Syracuse, NY 13210. E-mail anumonwj{at}upstate.edu
The inwardly rectifying potassium (Kir) 2.x channels mediate the cardiac inward rectifier potassium current (IK1). In addition to differences in current density, atrial and ventricular IK1 have differences in outward current profiles and in extracellular potassium ([K+]o) dependence. The whole-cell patch-clamp technique was used to study these properties in heterologously expressed Kir2.x channels and atrial and ventricular IK1 in guinea pig and sheep hearts. Kir2.x channels showed distinct rectification profiles: Kir2.1 and Kir2.2 rectified completely at potentials more depolarized than –30 mV (I
0 pA). In contrast, rectification was incomplete for Kir2.3 channels. In guinea pig atria, which expressed mainly Kir2.1, IK1 rectified completely. In sheep atria, which predominantly expressed Kir2.3 channels, IK1 did not rectify completely. Single-channel analysis of sheep Kir2.3 channels showed a mean unitary conductance of 13.1±0.1 pS in 15 cells, which corresponded with IK1 in sheep atria (9.9±0.1 pS in 32 cells). Outward Kir2.1 currents were increased in 10 mmol/L [K+]o, whereas Kir2.3 currents did not increase. Correspondingly, guinea pig (but not sheep) atrial IK1 showed an increase in outward currents in 10 mmol/L [K+]o. Although the ventricles of both species expressed Kir2.1 and Kir2.3, outward IK1 currents rectified completely and increased in high [K+]o-displaying Kir2.1-like properties. Likewise, outward current properties of heterologously expressed Kir2.1-Kir2.3 complexes in normal and 10 mmol/L [K+]o were similar to Kir2.1 but not Kir2.3. Thus, unique properties of individual Kir2.x isoforms, as well as heteromeric Kir2.x complexes, determine regional and species differences of IK1 in the heart.
Key Words: Kir2 • extracellular potassium • heteromerization • rectification
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