ATP-sensitive potassium channels and efaroxan-induced insulin release in the electrofusion-derived BRIN-BD11 beta-cell line

The properties of ATP-sensitive K+ (K-ATP) channels were explored in the el ectrofusion-derived, glucose-responsive, insulin-secreting cell line BRIN-B D11 using patch-clamp techniques. In intact cells, K-ATP channels were inhi bited by glucose, the sulfonylurea tolbutamide, and the imidazoline compoun ds efaroxan and phentolamine, Each of these agents initiated insulin secret ion and potentiated the actions of glucose. K-ATP channels were blocked by ATP in a concentration-dependent manner and activated by ADP in the presenc e of ATP. In both intact cells and excised inside-out patches, the K-ATP ch annel agonists diazoxide and pinacidil activated channels, and both compoun ds inhibited insulin secretion evoked by glucose, tolbutamide, and imidazol ines. The mechanisms of action of imidazolines were examined in more detail . Pre-exposure of BRIN-BD11 cells to either efaroxan or phentolamine select ively inhibited imidazoline-induced insulin secretion but not the secretory responses of cells to glucose, tolbutamide, or a depolarizing concentratio n of KCI. These conditions did not result in the loss of depolarization-dep endent rises in intracellular Ca2+ ([Ca2+](i)), K-ATP channel operation, or the actions of either ATP or efaroxan on K-ATP channels. Desensitization o f the imidazoline receptor following exposure to high concentrations of efa roxan, however, was found to result in an increase in SUR1 protein expressi on and, as a consequence, an upregulation of K-ATP channel density. Our dat a protide 1) the first characterization of K-ATP channels in BRIN-BD11 cell s, a novel insulin-secreting cell Line produced by electrofusion techniques , and 2) a further analysis of the role of imidazolines in the control of i nsulin release.