Inhibition of large conductance calcium-dependent potassium channel by Rho-kinase contributes to agonist-induced vasoconstriction

Abstract

We tested the hypothesis that Rho-kinase inhibits the large-conductance, calcium and voltage dependent potassium (BK_Ca) channels thereby promoting vasoconstriction. Our results show that the Rho-kinase inhibitor, Y-27632, induced concentration-dependent relaxation in rat mesenteric artery. The selective BK_Ca channel inhibitors, iberiotoxin (0.1 mM) and tetraethylammonium (10 mM) increased the EC₅₀ of Y-27632 more than 2-fold and decreased Y-27632-induced maximum relaxation (P<0.05). In the inside-out patch clamp configuration, constitutively active Rho-kinase (1mg/ml) attenuated BK_Ca channel activity induced by protein kinase G (PKG) (P<0.05). Y-27632 (10 mM) reversed the inhibitory effect of active Rhokinase (P<0.01). Furthermore, in the presence of Y-27632, addition of active Rho-kinase had no effect on PKG-stimulated BKCa channel activity. Taken together, our data suggest that Rho-kinase negatively regulates BK_Ca channels, thus providing a novel mechanism though which Rho-kinase increases smooth muscle contraction.

Keywords: Rho, smooth muscle, hyperpolarization, vascular reactivity, mesenteric artery, patch clamp