Influence of the murine diabetes gene on rubidium ion efflux from perifused islets

Islets from diabetic C57BL/KsJ db/db mice and normal C57BL/KsJ +/+ mice were loaded with 86Rb+ and micro-perfused with nonradioactive medium for 25 min. The appearance of 86Rb+ in the effluent could be described as the sum of two exponential functions with difference proportionality constants. The rapid efflux component may have represented washout from the extracellular space, and had about the same proportionality constant in normal and diabetic mice. The slow efflux component probably reflected efflux across the islet cell plasma membranes. At 3 mmol/l D-glucose in the medium, the slow efflux was significantly retarded in diabetic as compared with normal mice. In normal mice, but not in diabetics, 20 mmol/l D-glucose inhibited the slow efflux component. It is concluded that the basal K+ permeability is decreased in KsJ db/db mouse islet cells, and that this abnormality may explain their persistant depolarization at low glucose concentrations.