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J Mol Cell Cardiol. 2015 Jul;84:52-60. doi: 10.1016/j.yjmcc.2015.04.010. Epub 2015 Apr 15.

Regional variation of the inwardly rectifying potassium current in the canine heart and the contributions to differences in action potential repolarization.

Author information

1
Department of Experimental Cardiology, Masonic Medical Research Laboratory, Utica, NY, United States.
2
Department of Physiology and Biophysics, State University of New York, University of Buffalo, Buffalo, NY, United States.
3
Division of Biomedical Sciences, School of Medicine, University of California, Riverside, Riverside, CA, United States.
4
Department of Physiology and Biophysics, State University of New York, University of Buffalo, Buffalo, NY, United States; Department of Obstetrics and Gynecology, State University of New York, University of Buffalo, Buffalo, NY, United States.
5
Department of Experimental Cardiology, Masonic Medical Research Laboratory, Utica, NY, United States. Electronic address: panamab@mmrl.edu.

Abstract

The inward rectifier potassium current, IK1, contributes to the terminal phase of repolarization of the action potential (AP), as well as the value and stability of the resting membrane potential. Regional variation in IK1 has been noted in the canine heart, but the biophysical properties have not been directly compared. We examined the properties and functional contribution of IK1 in isolated myocytes from ventricular, atrial and Purkinje tissue. APs were recorded from canine left ventricular midmyocardium, left atrial and Purkinje tissue. The terminal rate of repolarization of the AP in ventricle, but not in Purkinje, depended on changes in external K(+) ([K(+)]o). Isolated ventricular myocytes had the greatest density of IK1 while atrial myocytes had the lowest. Furthermore, the outward component of IK1 in ventricular cells exhibited a prominent outward component and steep negative slope conductance, which was also enhanced in 10 mM [K(+)]o. In contrast, both Purkinje and atrial cells exhibited little outward IK1, even in the presence of 10 mM [K(+)]o, and both cell types showed more persistent current at positive potentials. Expression of Kir2.1 in the ventricle was 76.9-fold higher than that of atria and 5.8-fold higher than that of Purkinje, whereas the expression of Kir2.2 and Kir2.3 subunits was more evenly distributed in Purkinje and atria. Finally, AP clamp data showed distinct contributions of IK1 for each cell type. IK1 and Kir2 subunit expression varies dramatically in regions of the canine heart and these regional differences in Kir2 expression likely underlie regional distinctions in IK1 characteristics, contributing to variations in repolarization in response to in [K(+)]o changes.

KEYWORDS:

Atria; Electrophysiology; Potassium channel; Purkinje; Ventricle

PMID:
25889894
PMCID:
PMC4468020
DOI:
10.1016/j.yjmcc.2015.04.010
[Indexed for MEDLINE]
Free PMC Article

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