Single voltage-dependent K+ and Cl- channels in cultured rat astrocytes.

The kinetic reactions of a voltage-dependent K+ channel, which constituted about 14% of all the recorded K+ channels in the membrane of cultured rat astrocytes were studied in detail. A scheme of one open and three closed states is necessary to describe the kinetic reactions of this channel. The channel contributes little to the resting membrane potential. Its steady state open probability (Po) is 0.06 at -70 mV. When the cell is depolarized to O mV, Po approaches 1. This represents a 17-fold increase. Such channels could contribute to the potassium clearance by enhancing the effect of "spatial buffering." Additionally, single anion-selective channels with very high conductances were found in inside-out patches in approximately 15% of all recorded channels in the membrane of rat astrocytes. Channel openings are characterized by more than one conductance level; the main level showed a mean conductance of 400 pS. These channels are divided into two groups. Approximately 90% of the recorded chloride channels showed a strong voltage dependency of their current fluctuations. Within a relatively small potential range (+/- 15 mV) the channels have a high probability of being in the active state. After a voltage jump to varying testing potentials in the range of +/- 20 to +/- 50 mV the channels continued to be in the active state for some time and then closed to a shut state. If the testing potential persisted, the channels were not able to leave this shut state.(ABSTRACT TRUNCATED AT 250 WORDS)