ATP-SENSITIVE K+ CHANNELS FROM AORTIC SMOOTH-MUSCLE INCORPORATED INTO PLANAR LIPID BILAYERS

Glibenclamide binding sites were identified in a membrane preparation from canine aortic smooth muscle. The dissociation constant for [H-3]glibenclamide binding was 10 +/- 2 nM, with a density of 420 +/- 108 fmol/mg protein. The properties of ATP-sensitive potassium (K(ATP)) channels from the same membrane preparation incorporated into planar lipid bilayers were investigated. ATP was a potent inhibitor of the channels with half-maximal inhibition of channel activity by 41-mu-M ATP. Glibenclamide inhibited channel activity, and cromakalim activated the channel in the presence of ATP. Blockers of Ca2+-activated K+ (K(Ca)) channels (charybdotoxin and tetraethylammonium ions) did not affect K(ATP) channels in concentrations that caused significant block of K(Ca) channels in bilayers. This membrane preparation should allow further biochemical and functional characterization of K(ATP) channels and glibenclamide receptors in arterial smooth muscle.