Potassium and Chloride Fluxes Are Involved in Volume Regulation in Mouse Pancreatic Islet Cells

Potassium and chloride transport were measured in beta-cell-rich islets from ob/ob-mice using 36Cl- and 86Rb+ (K+-analogue). Reduction of the osmolarity from the normal 317 mosm l-1 to 180 mosm l-1 reduced the apparent content of K+ and Cl-. Hypo-osmolarity had no effect on the ouabain-sensitive portion of the Rb+ influx (Na+/K+ pump), but reduced the ouabain-resistant portion of the influx. Hypo-osmolarity also strongly increased the Rb+ efflux rate. Both tetracaine (0.5 mM) and glibenclamide (20 microM), which increase the osmotic resistance of pancreatic beta cells, significantly potentiated the reduction in apparent K+ content induced by hypo-osmolarity. This study suggests that the volume regulation in pancreatic beta cells is partly due to K+ and Cl- flux and that glibenclamide and tetracaine increase the osmotic resistance of the beta cells by affecting such ion transport.