Pharmacology of human sulphonylurea receptor SUR1 and inward rectifier K+ channel Kir6.2 combination expressed in HEK‐293 cells

The pharmacological properties of KATP channels generated by stable co‐expression of the sulphonylurea receptor SUR1 and the inwardly rectifying K+ channel Kir6.2 were characterized in HEK‐293 cells. [3H]‐Glyburide (glibenclamide) bound to transfected cells with a Bmax value of 18.5 pmol mg−1 protein and with a KD value of 0.7 nM. Specific binding was displaced by a series of sulphonylurea analogues with rank order potencies consistent with those observed in pancreatic RINm5F insulinoma and in the brain. Functional activity of KATP channels was assessed by whole cell patch clamp, cation efflux and membrane potential measurements. Whole cell currents were detected in transfected cells upon depletion of internal ATP or by exposure to 500 μM diazoxide. The currents showed weak inward rectification and were sensitive to inhibition by glyburide (IC50=0.92 nM). Metabolic inhibition by 2‐deoxyglucose and oligomycin treatment triggered 86Rb+ efflux from transfected cells that was sensitive to inhibition by glyburide (IC50=3.6 nM). Diazoxide, but not levcromakalim, evoked concentration‐dependent decreases in DiBAC4(3) fluorescence responses with an EC50 value of 14.1 μM which were attenuated by the addition of glyburide. Diazoxide‐evoked responses were inhibited by various sulphonylurea analogues with rank order potencies that correlated well with their binding affinities. In summary, results from ligand binding and functional assays demonstrate that the pharmacological properties of SUR1 and Kir6.2 channels co‐expressed in HEK‐293 cells resemble those typical of native KATP channels described in pancreatic and neuronal tissues. British Journal of Pharmacology (2000) 129, 1323–1332; doi:10.1038/sj.bjp.0703181