Single voltage-dependent K+-channels in cultured astrocytes

The open-occupation time of about 35% of the K+ channels in astrocytes increases strongly with depolarization. The kinetics of one of three different types of voltage-dependent channels (present in about 10% of all records) have been studied in detail. Openings can be fitted with one exponential, while a sum of three exponentials is necessary to fit the distributions of closures. A reaction scheme of one open and three closed states is necessary to describe the kinetic reactions of this channel. Voltage dependence is expressed by a strong increase of burst duration with depolarization. At resting potential (-70 mV), the channel contributes little to the resting membrane potential. Its steady-state open probability (P0) is 0.058. When the cell is depolarized, P0 can increase up to 0.96. Functionally, such channels could contribute to the potassium clearance by enhancing the effect of 'spatial buffering'.