Some properties of single potassium channels in cultured oligodendrocytes

Abstract

K⁺ channels were studied in oligodendrocytes in cultures of mouse spinal cord. Single channel currents were measured using the gigaseal technique. The conductance of the channels varied greatly i.e. from 6 to 125 pS (38±28 SD,N=21). In some patches there were up to three current levels of the same size. At −70 mV the open state probability was 0.51±0.17 and the average duration of an opening 70±20 ms for 4 channels with conductance from 16–57 pS. These analyses exclude brief flickering (less than 2 ms) or long closed periods (seconds to minutes). These times were not markedly affected by pulling the patch off the cell or by superfusing the isolated patch with media containing 10 mmol×1⁻¹ TEA or EGTA without Ca²⁺. At membrane potentials between −90 and −30 mV there was a small but consistent effect of depolarization to increase the open state probability. Large positive or negative voltage steps decreased the open state probability. Current voltage measurements on intact cells showed a striking decrease in membrane conductance at these large membrane potentials. The leakage conductance of the patch also exhibited some K⁺ selectivity. The oligodendrocyte membrane appears to contain about one K⁺ channel per 5 μm². The known electrical properties of cultured oligodendrocytes can essentially be explained by the distribution and properties of these K⁺ channels.