The ability of a new hypoglycaemic agent, A‐4166, compared to sulphonylureas, to increase cytosolic Ca 2+ in pancreatic β‐cells under metabolic inhibition

N ‐( trans ‐4‐isopropylcyclohexanecarbonyl)‐ d ‐phenylalanine (A‐4166) is a new non‐sulphonylurea oral hypoglycaemic agent which stimulates insulin release by increasing cytosolic Ca 2+ concentration ([Ca 2+ ] i ) in β‐cells. We studied comparative effects of A‐4166 and sulphonylureas on [Ca 2+ ] i , measured by dual‐wavelength fura‐2 microfluorometry, in single rat pancreatic β‐cells under normal conditions and conditions where glucose metabolism was inhibited. A glucokinase inhibitor, mannoheptulose (10 m m ), a mitochondrial respiratory inhibitor, KCN (100 μ m ), and uncouplers, dinitrophenol (DNP, 50 μ m ) and carbonyl cyanide p ‐trifluoromethoxyphenylhydrazone (FCCP, 0.3 μ m ), were used to abolish glucose‐induced increases in [Ca 2+ ] i in a reversible manner. Under control conditions, A‐4166 was one order more potent than tolbutamide in increasing [Ca 2+ ] i , and maximal responses were evoked by 30 μ m A‐4166 and 300 μ m tolbutamide. These equipotent concentrations were employed for the comparative study where glucose metabolism was inhibited. In the presence of mannoheptulose, [Ca 2+ ] i responses to tolbutamide, but not those to A‐4166, were attenuated in a reversible manner. KCN, DNP and FCCP inhibited [Ca 2+ ] i responses to tolbutamide to a much greater extent than those to A‐4166. Responses to tolbutamide even at 3.3 times the equipotent concentration (1000 μ m ) were also markedly attenuated by these inhibitors. Responses evoked by another sulphonylurea, gliclazide, were inhibited by DNP to a larger extent than A‐4166‐induced responses. The results indicate that A‐4166 acts more effectively than sulphonylureas to increase [Ca 2+ ] i in β‐cells during metabolic inhibition.British Journal of Pharmacology (1997) 120 , 1191–1198; doi: 10.1038/sj.bjp.0701017