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1 Department of Medicine and Research Center, Montreal Heart Institute, Montreal, Quebec H1T 1C8; 2 Department of Medicine, University of Montreal, Montreal, Quebec H3C 3J7; and Departments of 3 Pathology, 4 Pharmacology, and 5 Physiology, McGill University, Montreal, Quebec H3G 1Y6, Canada
Ventricular inward rectifier K+ current (IK1) is substantially larger than atrial, producing functionally important action potential differences. To evaluate possible molecular mechanisms, we recorded IK1 with patch-clamp techniques and studied Kir2.1 and Kir2.3 subunit expression. IK1 density was >10-fold larger in the canine ventricle than atrium. Kir2.1 protein expression (Western blot) was 78% greater (P < 0.01) in the ventricle, but Kir2.3 band density was 228% greater (P < 0.01) in the atrium. Immunocytochemistry showed transverse tubular localization of Kir2.1 in 89% (17 of 19) of ventricular and 26% (5 of 19, P < 0.0001) of atrial cells. Both exhibited a weakly positive Kir2.1 signal at intercalated disks. Kir2.3 was strongly expressed at the intercalated disks in all cells and in the transverse tubular regions in 78% (14 of 18) of atrial and 22% (4 of 18, P < 0.001) of ventricular cells. Tissue immunohistochemical results qualitatively resembled isolated cell data. We conclude that the expression density and subcellular localization of Kir2.1 and Kir2.3 subunits differ in the canine atrium versus ventricle. Overall protein density differences are insufficient to explain IK1 discrepancies, which may be related to differences in subcellular distribution.
inward rectifier potassium current; ion channels; cell biology; electrophysiology
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