Angiotensin II reduces the surface abundance of KV 1.5 channels in arterial myocytes to stimulate vasoconstriction.

Abstract

Several different voltage-dependent K+ (KV ) channel isoforms are expressed in arterial smooth muscle cells (myocytes). Vasoconstrictors inhibit KV currents, but the isoform selectivity and mechanisms involved are unclear. We show that angiotensin II (Ang II), a vasoconstrictor, stimulates degradation of KV 1.5, but not KV 2.1, channels through a protein kinase C- and lysosome-dependent mechanism, reducing abundance at the surface of mesenteric artery myocytes. The AngII-induced decrease in cell surface KV 1.5 channels reduces whole-cell KV 1.5 currents and attenuates KV 1.5 function in pressurized arteries. We describe a mechanism by which AngII stimulates protein kinase C-dependent KV 1.5 channel degradation, reducing the abundance of functional channels at the myocyte surface. Smooth muscle cells (myocytes) of resistance-size arteries express several different voltage-dependent K+ (KV ) channels, including KV 1.5 and KV 2.1, which regulate contractility. Myocyte KV currents are inhibited by vasoconstrictors, including angiotensinII (AngII), but the mechanisms involved are unclear. Here, we tested the hypothesis that AngII inhibits KV currents by reducing the plasma membrane abundance of KV channels in myocytes. AngiotensinII (applied for 2h) reduced surface and total KV 1.5 protein in rat mesenteric arteries. In contrast, AngII did not alter total or surface KV 2.1, or KV 1.5 or KV 2.1 cellular distribution, measured as the percentage of total protein at the surface. Bisindolylmaleimide (BIM; a protein kinaseC blocker), a protein kinaseC inhibitory peptide or bafilomycinA (a lysosomal degradation inhibitor) each blocked the AngII-induced decrease in total and surface KV 1.5. Immunofluorescence also suggested that AngII reduced surface KV 1.5 protein in isolated myocytes; an effect inhibited by BIM. Arteries were exposed to AngII or AngII plus BIM (for 2h), after which these agents were removed and contractility measurements performed or myocytes isolated for patch-clamp electrophysiology. AngiotensinII reduced both whole-cell KV currents and currents inhibited by Psora-4, a KV 1.5 channel blocker. AngiotensinII also reduced vasoconstriction stimulated by Psora-4 or 4-aminopyridine, another KV channel inhibitor. These data indicate that AngII activates protein kinaseC, which stimulates KV 1.5 channel degradation, leading to a decrease in surface KV 1.5, a reduction in whole-cell KV 1.5 currents and a loss of functional KV 1.5 channels in myocytes of pressurized arteries.