Electrical activity in pancreatic islet cells The VRAC hypothesis

A major aspect of stimulation of beta-cell function by glucose is the induction of electrical activity. The ionic events that underlie beta-cell electrical activity are understood in some detail. At sub-stimulatory glucose concentrations, the beta-cell is electrically 'silent'. Increasing the glucose concentration to stimulatory levels results in a gradual depolarization of the membrane potential to a threshold potential where 'spikes' or action potentials are generated. These action potentials represent the gating of voltage-sensitive Ca2+ channels, leading to Ca2+ entry into the cell, thus triggering the release of insulin. The stimulatory actions of glucose on the beta-cell depend on the metabolism of the hexose. A major question concerns the molecular mechanism(s) whereby beta-cell plasma membrane potential is regulated by changes in glucose metabolism in the cell. This article provides a brief summary of the evidence suggesting that, in addition to metabolically-regulated K-ATP channels, beta-cells are equipped with a volume-regulated anion channel that is activated by glucose concentrations within the range effective in modulating electrical activity and insulin release.