ATP-Dependent inhibition of Ca²⁺-activated K⁺ channels in vascular smooth muscle cells by neuropeptide Y

Abstract

Neuropeptide Y(NPY) inhibits Ca²⁺-activated K⁺ channels reversibly in vascular smooth muscle cells from the rat tail artery. NPY (200 μM) had no effect in the absence of intracellular adenosine 5′triphosphate (ATP) and when the metabolic poison cyanide-M-chlorophenyl hydrozone (10 μM) was included in the intracellular pipette solution. NPY was also not effective when ATP was substituted by the non-hydrolysable ATP analogue adenosine 5′-[β, γ-methylene]-triphosphate (AMP-PCP). NPY inhibited Ca²⁺-activated K⁺ channel activity when ATP was replaced by adenosine 5′-O-(3-thiotriphosphate) (ATP [γ-S]) and the inhibition was not readily reversed upon washing. Protein kinase inhibitor (1 μM), a specific inhibitor of adenosine 3′, 5′-cyclic monophosphatedependent protein kinase, had no significant effect on the inhibitory action of NPY. The effect of NPY on single-channel activity was inhibited by the tyrosine kinase inhibitor genistein (10 μM) but not by daidzein, an inactive analogue of genistein. These observations suggest that the inhibition by NPY of Ca²⁺-activated K⁺ channels is mediated by ATP-dependent phosphorylation. The inhibitory effect of NPY was antagonized by the tyrosine kinase inhibitor genistein.