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The Impact of ATP-Sensitive K⁺ Channel Subtype Selectivity of Insulin Secretagogues for the Coronary Vasculature and the Myocardium

From the Department of Pharmacology and Toxicology, Medical Faculty, University of Tübingen, Tübingen, Germany

Insulin secretagogues (sulfonylureas and glinides) increase insulin secretion by closing the ATP-sensitive K⁺ channel (K_ATP channel) in the pancreatic ß-cell membrane. K_ATP channels subserve important functions also in the heart. First, K_ATP channels in coronary myocytes contribute to the control of coronary blood flow at rest and in hypoxia. Second, K_ATP channels in the sarcolemma of cardiomyocytes (sarcK_ATP channels) are required for adaptation of the heart to stress. In addition, the opening of sarcK_ATP channels and of K_ATP channels in the inner membrane of mitochondria (mitoK_ATP channels) plays a central role in ischemic preconditioning. Opening of sarcK_ATP channels also underlies the ST-segment elevation of the electrocardiogram, the primary diagnostic tool for initiation of lysis therapy in acute myocardial infarction. Therefore, inhibition of cardiovascular K_ATP channels by insulin secretagogues is considered to increase cardiovascular risk. Electrophysiological experiments have shown that the secretagogues differ in their selectivity for the pancreatic over the cardiovascular K_ATP channels, being either highly selective (1,000x; short sulfonylureas such as nateglinide and mitiglinide), moderately selective (10–20x; long sulfonylureas such as glibenclamide [glyburide]), or essentially nonselective (<2x; repaglinide). New binding studies presented here give broadly similar results. In clinical studies, these differences are not yet taken into account. The hypothesis that the in vitro selectivity of the insulin secretagogues is of importance for the cardiovascular outcome of diabetic patients with coronary artery disease needs to be tested.

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