THE RESPONSE OF PANCREATIC β‐CELL MEMBRANE POTENTIAL TO POTASSIUM‐INDUCED CALCIUM INFLUX IN THE PRESENCE OF GLUCOSE

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Abstract
Membrane potential measurements were made in pancreatic .beta.-cells from microdissected islets from normal mice. In the presence of 11 mM glucose, depolarization of the membrane for 1 min with 50 mM K is followed by an inhibition of electrical activity before the normal burst pattern resumes. This inhibitory period, called the recovery time, is steady for each .beta.-cell after 3 consecutive pulses of 50 mM K. The mean recovery time is 109 s. During the recovery time, the membrane is hyperpolarized and the input resistance is decreased, indicating that K permeability is high over this period. The recovery time is dependent on the size of the depolarization: 1 min exposure to K concentrations below 50 mM reduces the recovery time with a half-maximal effect at 38.5 mM K, corresponding to -27 mV. Increasing the extracellular Ca concentration lengthens the recovery time. Increasing the glucose concentration shortens the recovery time. The recovery time represents activation of the Ca-gated K permeability and is a reflection of the time taken for the .beta.-cell to buffer the increased intracellular Ca resulting from the K depolarization.

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