Acetylcholine-induced current fluctuations in tissue-cultured muscle cells under voltage clamp

Acetylcholine applied ionophoretically to chick skeletal muscle cells grown in tissue culture produces membrane current fluctuations. Cells treated with vinblastine are transformed to a roughly spherical shape. Such transformed cells can be voltage-clamped with microelectrodes. The frequency spectrum of the current fluctuations at fixed voltage obeys a relation of the Lorentz form. From analysis of the current noise, the conductance of a single ionic channel is estimated to be 39 pmho at a temperature of 28 degrees C, and increases with increasing temperature, exhibiting a Q10 of 1.7. The relaxation time for the channel conductance is more sharply temperature dependent, showing a Q10 of approximately 5. These results are in agreement with the picture of acetylcholine-activated ionic channels determined from experiments on frog end plate (Anderson and Stevens, 1973). The relaxation time for carbachol activation is shorter than for acetylcholine, and appears to be more temperature sensitive.