Membrane potentials and input resistance were measured in beta-cells from mouse pancreatic islets of Langerhans in a study designed to assess the role of a K permeability specifically blocked by quinine or quinidine and activated by intracellular calcium ion concentration ([Ca2+])i-activated PK). 2. Addition of 100 microM-quinine to the perifusion medium resulted in a 10--30 mV depolarization of the membrane and an increase in the input resistance of ca. 4.10(7) omega. 3. In the absence of glucose, 100 microM-quinine induced electrical activity. 4. In the presence of glucose, 100 microM-quinine abolished the burst pattern of electrical activity and very much reduced the graded response of spike frequency normally seen with different concentrations of glucose. 5. Addition of mitochondrial inhibitors, KCN, NaN3, DNP, CCCP, FCCP, to the perifusion medium containing glucose rapidly hyperpolarized the beta-cell membrane, inducing a concomitant decrease in input resistance. 6. In the presence of glucose, these mitochondrial inhibitors reversibly blocked electrical activity; upon removal of the inhibitor, recovery of electrical activity followed a biphasic pattern. 7. The effects of mitochondrial inhibitors were partially reversed by 100 microM-quinine. 8. It is proposed that the membrane potential of the beta-cell in the absence of glucose is predominantly controlled by the [Ca2+]i-activated PK. It is further suggested that this permeability to K controls the level for glucose stimulation and leads to the generation of the burst pattern.
