The ability of a new hypoglycaemic agent, A-4166, compared to sulphonylureas, to increase cytosolic Ca2+ in pancreatic beta-cells under metabolic inhibition

1 N-(trans-4-isopropylcyclohexanecarbonyl)-D-phenylalanine (A-4166) is a new non-sulphonylurea oral hypoglycaemic agent which stimulates insulin release by increasing cytosolic Ca2+ concentration ([Ca2+](i)) in beta-cells. 2 We studied comparative effects of A-4166 and sulphonylureas on [Ca2+](i), measured by dual-wavelength fura-2 microfluorometry, in single rat pancreatic beta-cells under normal conditions and conditions where glucose metabolism was inhibited. 3 A glucokinase inhibitor, mannoheptulose (10 mM), a mitochondrial respiratory inhibitor, KCN (100 mu M), and uncouplers, dinitrophenol (DNP, 50 mu M) and carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP, 0.3 mu M), were used to abolish glucose-induced increases in [Ca2+](i) in a reversible manner. 4 Under control conditions, A-4166 was one order more potent than tolbutamide in increasing [Ca2+](i), and maximal responses were evoked by 30 mu M A-4166 and 300 mu M tolbutamide. These equipotent concentrations were employed for the comparative study where glucose metabolism was inhibited. 5 In the presence of mannoheptulose, [Ca2+](i) responses to tolbutamide, but not those to A-4166, were attenuated in a reversible manner. 6 KCN, DNP and FCCP inhibited [Ca2+](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 mu 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. 7 The results indicate that A-4166 acts more effectively than sulphonylureas to increase [Ca2+](i) in beta-cells during metabolic inhibition.