Acetylcholine noise in cultured chick myoballs: a voltage clamp analysis.

1. Large spherical muscle cells were grown in vitro by allowing dissociated chick myoblasts to fuse in suspension culture. 2. Myoball membranes could be adequately voltage clamped even in the face of large inward currents (ca. 100 nA) induced by ACh. 3. The single channel conductance, gamma, estimated from the ratio of the mean to the variance of ACh currents was 25-40 pmho at temperatures between 25 degrees and 37 degrees C. 4. Spectra of ACh current fluctuations declined with 1/f2. The mean channel open time (tau) estimated from the half-power frequency was 2 msec at 37 degrees C and -90 mV holding potential. At lower membrane potentials tau was decreased and on hyperpolarization tau was prolonged.