Evidence for two distinct potassium channels in avian granulosa cells

Single-channel potassium currents were recorded in avian granulosa cells using the patch-clamp technique. Two types of channel were observed. The smaller of the two channels, gK1, had a conductance of 15 to 30 picosiemens (pS) and was voltage- and calcium-independent. Its null-current potential was -50 mV in the cell-attached recording mode. The other channel, gK2, was infrequently observed in the cell-attached configuration. Its conductance was between 160 and 195 pS. It could be activated by calcium on the cytoplasmic side of the membrane patch in the inside-out configuration. It was also voltage-dependent. These results suggest that fast transmembrane potassium movements may be involved in the membrane voltage regulation of granulosa cells, which in turn may play an important role in the modulation of steroidogenesis and other metabolic activities.