PHARMACOLOGICAL CHARACTERIZATION OF THE SULFONYLUREA RECEPTOR IN RAT ISOLATED AORTA

1 The binding of the sulphonylurea [H-3]-glibenclamide, a blocker of a denosine 5'-triphosphate (ATP)-sensitive K+ channels (K-ATP channels), was studied in endothelium-denuded rings from rat aorta. 2 [H-3]-glib enclamide labelled two classes of binding sites with KD values of 20 /- 5 nM and 32 +/- 1 mu M. The high affinity component, which comprise d 17% of total binding at 1 nM [H-3]-glibenclamide, had an estimated b inding capacity of 150 fmol mg(-1) wet weight. 3 Other sulphonylureas such as glipizide and glibornuride and the sulphonylurea-related carbo xylate, AZ-DF 265, inhibited high affinity [H-3]-glibenclamide binding with the potencies expected from their K+ channel activity. At very h igh concentrations, AZ-DF 265 and glipizide started to interact also w ith the lour affinity component of [H-3]-glibenclamide binding. 4 Open ers of the ATP-sensitive K+ channel belonging to different structural groups inhibited only the high affinity [H-3]-glibenclamide binding; t he potencies in this assay were similar to those obtained in functiona l (i.e. vasorelaxation) studies. 5 High affinity [H-3]-glibenclamide b inding was abolished by prolonged hypoxia combined with metabolic inhi bition. 6 The data indicate that the high affinity component of [H-3]- glibenclamide binding mediates the block of the K-ATP channel by the s ulphonylureas in rat aorta; hence, it represents the sulphonylurea rec eptor in this vessel. The pharmacological properties of this binding s ite resemble those of the binding site for the openers of the K-ATP ch annel; present evidence suggests that these two classes of sites are n egatively allosterically coupled.