Characterization and solubilization of the sulphonylurea receptor in rat brain.
The binding characteristics of the sulphonylurea receptor were investigated using rat brain microsomes. Scatchard plots for binding of [3H]glibenclamide, a potent sulphonylurea which inhibits the ATP-sensitive K-channel, suggested the presence of both high and low affinity binding sites with Kd 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 Kd 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 microM and 130 microM, respectively. ATP and GTP inhibited [3H]glibenclamide binding in a Mg-dependent manner whereas the inhibition by ADP and GDP was Mg-independent [3H]Glibenclamide binding to the solubilized receptor was similarly inhibited by those nucleotides. Diazoxide inhibited [3H]glibenclamide binding in the presence of MgATP, but after CHAPS-solubilization diazoxide failed to inhibit [3H]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.
Niki
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Nuffield Department of Clinical Biochemistry, John Radcliffe Hospital, Headington, Oxford, U.K.
Ashcroft
S J
SJ
D018528:ATP-Binding Cassette Transporters; D000227:Adenine Nucleotides / Q000494:pharmacology; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D001549:Benzamides / Q000494:pharmacology; D001667:Binding, Competitive / Q000187:drug effects; D001923:Brain Chemistry / Q000187:drug effects*; D017301:Ca(2+) Mg(2+)-ATPase / Q000494:pharmacology; D003981:Diazoxide / Q000494:pharmacology; D005905:Glyburide / Q000493:pharmacokinetics / Q000494:pharmacology*; D006150:Guanine Nucleotides / Q000494:pharmacology; D007004:Hypoglycemic Agents / Q000494:pharmacology; D066298:In Vitro Techniques; D008566:Membranes / Q000378:metabolism; D008861:Microsomes / Q000187:drug effects / Q000378:metabolism*; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D024661:Potassium Channels, Inwardly Rectifying; D051381:Rats; D011955:Receptors, Drug / Q000187:drug effects / Q000378:metabolism*; D064233:Sulfonylurea Receptors; D014044:Tolbutamide / Q000494:pharmacology
D018528:ATP-Binding Cassette Transporters; D000227:Adenine Nucleotides; D001549:Benzamides; D006150:Guanine Nucleotides; D007004:Hypoglycemic Agents; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D011955:Receptors, Drug; D064233:Sulfonylurea Receptors; C030516:meglitinide; D014044:Tolbutamide; D000251:Adenosine Triphosphatases; D017301:Ca(2+) Mg(2+)-ATPase; D003981:Diazoxide; D005905:Glyburide