Influence of ethanol and acetaldehyde on electro-mechanical coupling of skeletal muscle fibers.

The effects of ethanol were studied on the time course of the isometric twitch and tetanus of isolated semitendinosus muscle fibers of Rana temporaria (at 2.8-4.5 degrees C). Ethanol in concentrations between (0.1-0.4 M) suppressed the isometric twitch without significantly affecting the tetanic tension amplitude. A further increase in ethanol concentration (0.5 M) depressed the tetanic tension as well. The maximum rate of force development both of twitch and tetanus was reduced. These changes were fully reversible when ethanol was removed from the bathing fluid. In presence of ethanol there was a reduction, although not statistically significant, in the resting membrane potential and in the maximum rate of rise of the action potential. The overshoot and the maximum rate of fall of the action potential were significantly lowered leading to a prolongation of the duration of the action potential. Acetaldehyde in relatively low concentrations (0.9-1.8 mM) caused marked potentiation of the twitch without significantly affecting the tetanic amplitude. These changes were, to a great extent, reversible. Higher concentrations (18 mM) of acetaldehyde reduced both the twitch and the tetanic tension and these effects were not reversible on removal of drug from the bathing solution. No detectable effects of the drug (1.8 mM) were observed on resting or action membrane potentials of the muscle fibre. The data presented supports the idea that ethanol suppresses the twitch response by inhibiting the calcium release mechanism and uncouples the excitation-contraction process. The twitch potentiation by acetaldehyde seems to be due to enhancement of calcium release from the storage sites.