THE SULFONYLUREA RECEPTOR CONFERS DIAZOXIDE SENSITIVITY ON THE INWARDLY RECTIFYING K-CELLS( CHANNEL KIR6.1 EXPRESSED IN HUMAN EMBRYONIC KIDNEY)

1. We have examined the effects of diazoxide and intracellular ATP (AT P(i)) on whole-cell currents in HEK293 cells transfected transiently w ith the inwardly rectifying K+ channel Kir6.1 (uKATP1) or cotransfecte d with Kir6.1 and the sulphonylurea receptor (SUR1). 2. Kir6.1 current s were unaffected by the K+ channel opener diazoxide or by dialysis wi th 0.3 mM ATP. 3. Kir6.1-SUR1 currents increased in amplitude when cel ls were dialysed with 0.3 mM ATP, but not with 5 mM ATP. This activati on may be explained by the loss of endogenous ATP from the cell when t he intracellular solution contains 0.3 mM ATP. Kir6.1-SUR1 currents we re also activated by diazoxide; this activation was greater with 0.3 m M ATP(i) than with 5 mM ATP(i). 4. We conclude that SUR1 is required t o confer both diazoxide and ATP sensitivity on Kir6.1.