CHARACTERIZATION AND SOLUBILIZATION OF THE SULFONYLUREA RECEPTOR IN RAT-BRAIN

The binding characteristics of the sulphonylurea receptor were investigated using rat brain microsomes. Scatchard plots for binding of [H-3]glibenclamide, a potent sulphonylurea which inhibits the ATP-sensitive K-channel, suggested the presence of both high and low affinity binding sites with K(d) of 0.58 and 17 nM, and beta(max) of 123 and 392 fmol/mg protein, respectively. When brain microsomes were solubilized with CHAPS, high affinity sites were retained with K(d) and beta(max) of 1.2 nM and 42.1 fmol/mg protein, respectively, whereas the low affinity sites disappeared. The specific binding was displaced by non-labelled glibenclamide, meglitinide, and tolbutamide with IC50 at 5 nM, 25 muM and 130 muM, respectively. ATP and GTP inhibited [H-3]glibenclamide binding in a Mg-dependent manner whereas the inhibition by ADP and GDP was Mg-independent. [H-3]Glibenclamide binding to the solubilized receptor was similarly inhibited by those nucleotides. Diazoxide inhibited [H-3]glibenclamide binding in the presence of MgATP, but after CHAPS-solubilization diazoxide failed to inhibit [H-3]glibenclamide binding even with MgATP. These findings suggest the brain sulphonylurea receptor has similar features to the beta-cell receptor. However, inhibition of the binding by nucleotides is not identical, possibly reflecting differences in the nucleotide-binding subunit.