Glucose-induced electrical activity in rat pancreatic β-cells:: dependence on intracellular chloride concentration

A rise in glucose concentration depolarizes the beta-cell membrane potential leading to electrical activity and insulin release. It is generally believed that closure of K-ATP channels underlies the depolarizing action of glucose, though work from several laboratories has indicated the existence of an additional anionic mechanism. It has been proposed that glucose activates a volume-regulated anion channel, generating an inward current due to Cl- efflux. This mechanism requires that intracellular [Cl-] is maintained above its electrochemical equilibrium. This hypothesis was tested in rat beta-cells by varying [Cl-] in the patch pipette solution using the Cl--permeable antibiotic amphotericin B to allow Cl- equilibration with the cell interior. Under such conditions, a depolarization and electrical activity could be evoked by 16 nm glucose with pipette solutions containing 80 or 150 mm Cl-. At 40 or 20 mm Cl-, a subthreshold depolarization was usually observed, whilst further reduction to 12 or 6 mm abolished depolarization, in some cases leading to a glucose-induced hyperpolarization. With a pipette solution containing gramicidin, which forms Cl--impermeable pores, glucose induced a depolarization and electrical activity irrespective of [Cl-] in the pipette solution. Under the latter conditions, glucose-induced electrical activity was prevented by bumetanide, an inhibitor of the Na+-K+-2Cl(-) co-transporter. This inhibition could be overcome by the use of amphotericin B with a high [Cl-] pipette solution. These findings suggest that the maintenance of high intraceflular [Cl-] in the beta-cell is an important determinant in glucose-induced depolarization, and support the hypothesis that beta-cell stimulation by glucose involves activation of the volume-regulated anion channel and generation of an inward Cl- current.