Pharmacological characterization of the sulphonylurea receptor in rat isolated aorta.
1. The binding of the sulphonylurea [3H]-glibenclamide, a blocker of adenosine 5'-triphosphate (ATP)-sensitive K+ channels (KATP channels), was studied in endothelium-denuded rings from rat aorta. 2. [3H]-glibenclamide labelled two classes of binding sites with KD values of 20 +/- 5 nM and 32 +/- 1 microM. The high affinity component, which comprised 17% of total binding at 1 nM [3H]-glibenclamide, had an estimated binding capacity of 150 fmol mg-1 wet weight. 3. Other sulphonylureas such as glipizide and glibornuride and the sulphonylurea-related carboxylate, AZ-DF 265, inhibited high affinity [3H]-glibenclamide binding with the potencies expected from their K+ channel activity. At very high concentrations, AZ-DF 265 and glipizide started to interact also with the low affinity component of [3H]-glibenclamide binding. 4. Openers of the ATP-sensitive K+ channel belonging to different structural groups inhibited only the high affinity [3H]-glibenclamide binding; the potencies in this assay were similar to those obtained in functional (i.e. vasorelaxation) studies. 5. High affinity [3H]-glibenclamide binding was abolished by prolonged hypoxia combined with metabolic inhibition. 6. The data indicate that the high affinity component of [3H]-glibenclamide binding mediates the block of the KATP channel by the sulphonylureas in rat aorta; hence, it represents the sulphonylurea receptor in this vessel. The pharmacological properties of this binding site resemble those of the binding site for the openers of the KATP channel; present evidence suggests that these two classes of sites are negatively allosterically coupled.
Löffler
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Department of Pharmacology, Medical Faculty, University of Tübingen, Germany.
Quast
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D000255:Adenosine Triphosphate / Q000502:physiology; D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects / Q000378:metabolism*; D001667:Binding, Competitive / Q000187:drug effects; D005905:Glyburide / Q000378:metabolism / Q000494:pharmacology; D007004:Hypoglycemic Agents / Q000378:metabolism / Q000494:pharmacology; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism*; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D011955:Receptors, Drug / Q000187:drug effects / Q000378:metabolism*; D013453:Sulfonylurea Compounds / Q000378:metabolism* / Q000494:pharmacology
D007004:Hypoglycemic Agents; D015221:Potassium Channels; D011955:Receptors, Drug; D013453:Sulfonylurea Compounds; D000255:Adenosine Triphosphate; D005905:Glyburide