Effects of the hypoglycaemic drugs repaglinide and glibenclamide on ATP-sensitive potassium-channels and cytosolic calcium levels in beta TC3 cells and rat pancreatic beta cells.

The present study demonstrates the action of the hypoglycaemic drugs repaglinide and glibenclamide in cultured newborn rat islet cells and mouse beta TC3 cells. In cell-attached membrane patches of newborn rat islet cells repaglinide (10 nmol/l) and glibenclamide (20 nmol/l) decrease the open probability of single ATP-sensitive K(+)-channels to approximately 10% of the activity prior to addition of the drugs in short-term experiments (< 5 min). The influence of repaglinide and glibenclamide on the ATP-sensitive K+ current was studied using the whole-cell patch clamp configuration. A half-maximal steady-state inhibition of the ATP-sensitive K+ currents is observed at 89 pmol/l repaglinide and at 47 pmol/l glibenclamide in whole-cell experiments of longer duration (30 min). Applying digital Ca2+ imaging on single beta TC3 cells we found that repaglinide and glibenclamide induced a concentration-dependent increase in intracellular free Ca2+ concentration ([Ca2+]i) with a half-maximal effect at 0.5 nmol/l for both drugs in long-term experiments (30 min). The rise in [Ca2+]i results from Ca2+ entry through voltage-dependent L-type Ca(2+)-channels since it is inhibited by verapamil (10 mumol/l). The effect of repaglinide and glibenclamide is partly reversible (approximately 80%).