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

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Abstract
Spontaneous electrical fluctuations (.+-. 0.2-0.4 mV) were recorded in quiescent atrial fibers of the carp. The noise decreased in acetylcholine, small hyperpolarization and EGTA [ethylene glycol tetraacetic acid]. The noise increased (to .+-. 1-2 mV) and became more synchronous in K+-free Ringer solution and in ouabain. Large voltage fluctuations (.+-. 1-2 mV) were accompanied by a fine mechanical tremor, indicating intracellular [Ca2+] fluctuations. 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. Intracellular [Ca2+] and the membrane K+-conductance are probably involved in a feedback loop which oscilates and produces electromechanical noise. The frequency of oscillation is determined by the relatively slow diffusion of Ca2+ from the intracellular reservoir to the surface membrane.