Enhanced single-channel K+ current in arterial membranes from genetically hypertensive rats

Arterial smooth muscle from hypertensive rats shows an increased membrane permeability to K+ that depends on Ca2+ influx. To define the mechanism of this membrane alteration, we tested the hypothesis that Ca(2+)-dependent K+ current (IK(Ca)) is increased in arterial muscle membranes from genetically hypertensive rats. Single-channel K+ currents measured in cell-attached and inside-out aortic membrane patches from spontaneously hypertensive rats (SHR) were compared with those from normotensive Wistar-Kyoto rats (WKY). Inside-out patches from both rat strains showed a predominant 225 pS, Ca(2+)- and voltage-dependent K+ channel in symmetrical 145 mM KCl solutions, which was blocked by tetraethylammonium [concentration for half-maximal block (IC50) < or = 0.3 mM]. In cell-attached patches of aortic muscle cells bathed in physiological salt solution, this channel [IK(Ca) channel] showed a fivefold higher open-state probability (NPo) in SHR as compared with WKY. This increased NPo of SHR IK(Ca) channels in membranes of intact aortic muscle cells was not correlated with an altered membrane potential in current-clamped SHR myocytes or with changes in cytosolic free Ca2+ concentration in fura-2-loaded aortic muscle cells. However, inside-out aortic membrane patches from SHR showed more detected IK(Ca) channels per patch, a higher IK(Ca) channel NPo, and a greater total patch current than their WKY counterparts. Further analysis revealed a greater Ca2+ sensitivity of SHR than WKY IK(Ca) channels. These results suggest that IK(Ca) channel function is altered in isolated membrane patches of arterial muscle from genetically hypertensive rats.(ABSTRACT TRUNCATED AT 250 WORDS)