Electrical characteristics of pancreatic islet cells

1. The electrical properties of mouse pancreatic islet cells have been explored in vitro using a single intracellular micro-electrode for both voltage recording and current injection. 2. The frequency of spontaneous electrical activity induced in islet cells by concentrations of D-glucose greater than 2-8 mM was enhanced by depolarizing, and reduced by hyperpolarizing, current injection. Post-stimulus inhibition and facilitation were also observed. 3. Intracellular current injection evoked a spike potential in Krebs solution containing a low D-glucose concentration (2-8mM), and in glucose-free, but not Ca-free solution. Evoked spikes were observed in approximately 10% of the cell population impaled. 4. The relationship between the rate of rise of an evoked spike and membrane potential displacement by intracellular current injection a sigmoid curve suggesting the presence of an inactivation process in spike potential genesis. 5. High [K]o, 30-50mM, induced electrical activity rarely, and then only transiently, thereafter blocking it; conditioning hyperpolarizing current tended to restore spike activity. 6. D-600, 5 times 10-minus 5M, blocked the electrical activity induced by D-glucose, tolbutamide or current injection; these inhibitory effects were reversed by a threefold increase in [Ca]o to 7-68 mM. 7. From these results it is concluded that the electrical activity induced in islet cells by Dglucose, tolbutamide and current injection is due mainlu to Ca-2+ influx and is dependent on the level of the membrane potential