Characterization of low-affinity binding sites for glibenclamide on the Kir6.2 subunit of the beta-cell K-ATP channel

The ATP-sensitive K+ channel, an octameric complex of two structurally unre lated types of subunits, SUR1 and Kir6.2, plays a central role in the physi ological regulation of insulin secretion. The sulfonylurea glibenclamide, w hich trigger insulin secretion by blocking the ATP-sensitive K+ channel, in teracts with both high and low affinity binding sites present on beta-cells . The high affinity binding site has been localized on SUR1 but the molecul ar nature of the low affinity site is still uncertain. In this study, we an alyzed the pharmacology of glibenclamide in a transformed COS-7 cell line e xpressing the rat Kir6.2 cDNA and compared with that of the MIN6 beta cell line expressing natively both the Kir6.2 and the SUR1 subunits. Binding stu dies and Scatchard analysis revealed the presence of a single class of low affinity binding sites for glibenclamide on the COS/Kir6.2 cells with chara cteristics similar to that observed for the low affinity site of the MIN6 b eta cells. (C) 1999 Academic Press.