Evidence for a differential cellular distribution of inward rectifier K channels in the rat isolated mesenteric artery

The distribution of functionally active, inwardly rectifying K (K-IR) channels was investigated in the rat small mesenteric artery using both freshly isolated smooth muscle and endothelial cells and small arterial segments. In Ca2+-free solution, endothelial cells displayed a K-IR current with a maximum amplitude of 190 +/- 16 pA at -150 mV and sensitivity to block with 30 muM Ba2+ (n = 7). In smooth muscle cells, outward K current was activated at around -47 +/- 3 mV, but there was no evidence of KIR current (n = 6). Furthermore, raising extracellular [K+] to either 60 or 140 mM, or applying the alpha(1)-adrenoceptor agonist phenylephrine (PE; 30 muM), failed to reveal an inwardly rectifying current in the smooth muscle cells, although PE did stimulate an iberiotoxin-sensitive outward K current (n = 4). Exogenous K+ (10.8-16.8 mM) both relaxed and repolarized endothelium-denuded segments of the mesenteric artery contracted with PE. These effects were depressed by 100 muM ouabain but unaffected by either 30 muM BaCl2 or 3 muM glibenclamide. These data suggest that functional, inwardly rectifying Ba2+-sensitive channels are restricted to the endothelial cell layer in the rat small mesenteric artery. Copyright (C) 2003 S. Karger AG, Basel.