Characteristics of the Ca channel from pancreatic B-cells and its modulation by glucose

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Voltage-dependent Ca channels were studied with regard to glucose modulation in rat pancreatic B-cells. The single channel conductance was 28 pS at 55 mM Ba on the external side of the cell-attached patch membrane. In an effort to exclude the effects on the Ca channels of membrane potential changes due to closure of ATP-sensitive K channels by glucose metabolism, the resting membrane potential was chemically clamped at 0 mV by bathing the cell in the high K internal solution. The open-state probability of the Ca channels was increased 2-3 fold with an increase in glucose concentration for either 2.8 or 5.6 mM to 16.7 mM. Consistent effects of glucose on the channels were obtained in the presence of 1 mu M BAY K 8644. An open time histogram consisted of a single exponentia1 curve with a time constant of 0.2 ms and 0.29 ms at glucose concentration of 5.6 mM and 22.4 mM. respectively. Two time constants were required in the closed time histogram and they were 0.82 ms and 18.9 ms at 5.6 mM gucose. and 0.91 ms and 5.05 ms at 22.4 mM glucose. These results suggest that Ca-channel gating may be modulated by glucose metabolism.