Mechanism of rapid K(+)-induced swelling of mouse astrocytes.

Cultured astrocytes from newborn mouse cortex were impaled with double-barrelled ion-sensitive microelectrodes to investigate their response following a 5 min exposure period to saline containing 60 mM K+. The membrane potential decreased from -74 to -11 mV, the intracellular K+ concentration increased from 102 to 145 mM and the intracellular pH increased from 7.05 to 7.60 indicating an increase in the HCO3- concentration from 9 to 31 mM. All changes were reversible. In additional series of experiments the cells were loaded with choline and the application of a bias current to electrodes containing the Corning 477317 resin made them more sensitive to choline than to K+. This resulted in a decrease of the ion potential during K+ exposure, which stabilized within 2 min. It is assumed that this is due to a dilution of intracellular choline by water intake. Thus, the early K(+)-evoked swelling response can be explained by a fast (approx. 2 min) swelling induced by K+ and HCO3- (and Cl-) influx.