The binding characteristics of the sulphonylurea receptor were investi
gated 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 bindi
ng sites with K(d) of 0.58 and 17 nM, and beta(max) of 123 and 392 fmo
l/mg protein, respectively. When brain microsomes were solubilized wit
h 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 affinit
y sites disappeared. The specific binding was displaced by non-labelle
d glibenclamide, meglitinide, and tolbutamide with IC50 at 5 nM, 25 mu
M 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 rec
eptor was similarly inhibited by those nucleotides. Diazoxide inhibite
d [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 recep
tor has similar features to the beta-cell receptor. However, inhibitio
n of the binding by nucleotides is not identical, possibly reflecting
differences in the nucleotide-binding subunit.