The intracellular Cl- activity (aCli) and the membrane potential (Vm) were simultaneously measured in cultured L-strain fibroblasts, using a Cl--selective liquid ion-exchanger microelectrode and a standard microelectrode. The oscillations of aCli and Vm were found to occur concomitantly. A decrease in the aCli value was associated with the spontaneous hyperpolarization. The depolarization produced by current injection resulted in an increase in aCli. These data suggest that the membrane permeability to Cl- is significantly high during the Vm oscillation in the L cell.
