Electromechanical noise in atrial muscle cells of the carp: a possible ionic feed-back mechanism.

1. Spontaneous electrical fluctuations (+/- 0.2-0.4 mV) were recorded in 'quiescent' atrial fibres of the carp. 2. The noise decreased in acetylcholine, small hyperpolarization and EGTA. 3. The noise increased (to +/- 1-2 mV) and became more synchronous in K+-free Ringer and in ouabain. 4. Large voltage fluctuations (+/- 1-2 mV) were accompanied by a fine mechanical tremor, indicating intracellular [Ca2+] fluctuations. 5. Spectral analysis showed a clear resonant frequency at about 1 Hz, indicating that the noise cannot result from the random switching of independent ionic channels. 6. We propose that the intracellular [Ca2+] and the membrane K+-conductance are involved in a feed-back loop which can oscillate and produce the electromechanical noise. The frequency of oscillation is determined by the relatively slow diffusion of Ca2+ from the intracellular reservoir to the surface membrane.