Pharmaco-topology of sulfonylurea receptors - Separate domains of the regulatory subunits of K-ATP channel isoforms are required for selective interaction with K+ channel openers

The differential responsiveness of (SUR1/K(IR)6.2)(4) pancreatic beta-cell versus (SUR2A/K(IR)6.2)(4) sarcolemmal or (SUR2B/K(IR)6.0)(4) smooth muscle cell K-ATP channels to K+ channel openers (KCOs) is the basis for the sele ctive prevention of hyperinsulinemia, myocardial infarction, nd acute hyper tension. KCO-stimulation of K-ATP channels is a unique example of functiona l coupling between a transport ATPase and a K+ inward rectifier. KCO bindin g to SUR is Mg-ATP-dependent and antagonizes the inhibition of (K(IR)6.0)(4 ) pore opening by nucleotides. Patch-clamping of matched chimeric human SUR 1-SUR2A/K(IR)6.2 channels was used to identify the SUR regions that specify the selective response of sarcolemmal versus beta-cell channels to cromaka lim or pinacidil versus diazoxide. The SUR2 segment containing the 12th thr ough 17th predicted transmembrane domains, TMD12-17, confers sensitivity to the benzopyran, cromakalim, and the pyridine, pinacidil, whereas an SUR1 s egment which includes TMD6-11 and the first nucleotide-binding fold, NBF1, controls responsiveness to the benzothiadiazine, diazoxide, These data are incorporated into a functional topology model for the regulatory SUR subuni ts of K-ATP channels.