Single channel currents were recorded from isolated membrane patches of cultured mouse oligodendrocytes using the giga-seal technique. The observed conductance of the channel was 71 ± 34 pS. Isolated patches contained 1 to 4 channels with similar conductances and kinetics. Closed timed of the channel varied from less than 1 msec to many minutes. The open state was always interrupted by flickering to the closed state. The kinetics of opening and closing appeared insensitive to voltage steps of up to ± 75 mV from the resting level of the membrane potential, but could be affected by very large voltage steps. The observed changes in channel current in response to changes of potassium concentration on either side of the membrane indicate a high selectivity for potassium. The results show a membrane with constant macroscopic permeability that contains channels which open and close.
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