Microdissected, β-cell-rich pancreatic islets from ob/ob mice were used in studies of 8 6 Rb + transport. D-Glucose (20 mM) induced a biphasic reduction in 8 6 R + efflux. The reduction stabilized within 10 min at 34% of the efflux rate at zero glucose. The initial 8 6 Rb + uptake (5 min) was dose-dependently reduced by ouabain with maximum inhibition at 1 mM. D-Glucose (20 mM) did not affect the ouabain-sensitive 8 6 Rb + influx but markedly reduced (48%) the ouabain-resistant isotope influx. The results suggest that D-glucose does not affect the Na + /K + pump in pancreatic β-cells and that the glucose-sensitive K + -transporting modalities (K + channels) in the β-cells can mediate both inward and outward K + flux.