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The Binding Properties of the Particulate and Solubilized Sulfonylurea Receptor from Cerebral Cortex Are Modulated by the Mg2+ Complex of ATP

Abstract: Glibenclamide closes an ATP‐sensitive K+ channel (K‐ATP channel) by interaction with the sulfonylurea receptor in the plasma membrane of pancreatic B cells and thereby initiates insulin release. Previous studies demonstrated that the Mg2+ complex of ATP decreases glibenclamide binding to the sulfonylurea receptor from pancreatic islets. The aim of the present study was to examine the effect of adenine and guanine nucleotides on binding of sulfonylureas to the cerebral sulfonylurea receptor. For this purpose, binding properties of the particulate and solubilized site from rat or pig cerebral cortex were analyzed. Maximum recovery of receptors in detergent extracts amounted to 40–50%. Specific binding of [3H]glibenclamide to the solubilized receptors corresponded well to specific binding to microsomes. In microsomes and detergent extracts, the Mg2+ complexes of ATP, ADP, GTP, and GDP inhibited binding of [3H]glibenclamide. These effects were not observed in the absence of Mg2+. In detergent extracts, Mg‐ATP (300 μM) reduced the number of high‐affinity sites for [3H]‐glibenclamide by 52% and increased the dissociation constant for [3H]glibenclamide by eightfold; Mg‐ATP was half‐maximally effective at 41 μM. Alkaline phosphatase accelerated the reversal of Mg‐ATP‐induced inhibition of [3H]glibenclamide binding. The data suggest similar control of the sulfonylurea receptor from brain and pancreatic islets by protein phosphorylation.