Biphasic action of ethanol on contraction of skeletal muscle

Ethanol (160-640 mM) produces a biphasic action on the indirectly stimulated rat phrenic nerve--diaphragm preparation. This consists of a potentiation followed by a blockade of muscle contraction. Concomitant with the increase in the force of contraction was the appearance of multiple neural action potentials recorded antidromically in response to a single nerve stimulation. In stimulated curarized muscle only blockade was observed. There was no difference in the degree of blockade between directly and indirectly stimulated preparations. We conclude that the potentiation of muscle contraction strength is produced by a facilitatory action of the drug on the motor nerve terminal and the blockade of contraction is produced by an action of the drug directly on the muscle fibers.