Potassium and rubidium permeability and potassium conductance of the beta-cell membrane in mouse islets of Langerhans.
The efflux of 42K+ and 86Rb+ has been studied in collagenase-isolated normal mouse islets of Langerhans. In double-labelled experiments, the ratio of efflux rate constants of Rb+ and K+ (kRb/kK) was 0.80 in 5 mM-K+ and 0 glucose. The ratio was unaffected by glucose concentrations up to 22.2 mM. In the presence of 50 mM-K+, 0 glucose, the ratio increased to 0.91 and in 50 mM-Rb+, 0 glucose and 0 K+, the ratio was 1.06. With these limitations, the results indicate that 86Rb+ is an acceptable isotope for K+. Using the Goldman model, K+ and Rb+ permeability coefficients and K+ slope and chord conductances were computed. The permeabilities decreased in glucose and in high K+ or high Rb+. In the case of high external K+, the K+ conductances increased. Also there may be more than one type of K+ channel with differing selectivities to K+ and Rb+. The addition of glucose in the presence of 50 mM-K+ had no further effect on Rb+ permeability. It is suggested that there are about ten small K+ channels open in the resting beta-cell and that progressive closure of these channels is involved in the depolarization of the cell membrane that initiates spike activity.
D000818:Animals; D002463:Cell Membrane Permeability; D004553:Electric Conductivity; D005947:Glucose / Q000494:pharmacology; D007515:Islets of Langerhans / Q000378:metabolism*; D051379:Mice; D009994:Osmolar Concentration; D011188:Potassium / Q000378:metabolism* / Q000494:pharmacology; D011197:Potassium Radioisotopes; D011868:Radioisotopes; D012413:Rubidium / Q000378:metabolism* / Q000494:pharmacology
D011197:Potassium Radioisotopes; D011868:Radioisotopes; D005947:Glucose; D012413:Rubidium; D011188:Potassium