The effects of sodium lauryl sulfate on the phrenic nerve diaphragm preparation from the rat

The time period to 50% inhibition of the twitches and compound action potential of the rat phrenic nerve-diaphragm preparation with sodium lauryl sulfate (2.5 x 10(-4)-5.0 x 10(-3)M) was recorded. The twitch contractions during indirect stimulation, the contraction during direct stimulation, and the compound action potential of the isolated phrenic nerve, were inhibited in that order. Depolarization due to high action potential activity induced by tetanic stimulation, veratridine, low Ca(2+)-or high K(+)-solutions, all enhanced the inhibitory effect of sodium lauryl sulfate (5.0 x 10(-4)M) during indirect stimulation. Hyperpolarization in K(+)-free solution and membrane stabilization by lidocaine antagonized the inhibitory effect of sodium lauryl sulfate. Accordingly, it probably induced inhibition by depolarization. The depolarization may decrease the influx of Ca2+ and the reuptake of choline+, as suggested by an observed synergism with tetraethylammonium CI and hemicholinium-3 Br, which antagonize the reuptake of choline+. On the opposite, 3,4-diaminopyridine, which increases the influx of Ca2+, antagonized the sodium lauryl sulfate-induced inhibition, and induced a biphasic contracture. The first phase was probably caused by a depolarization, and the second phase by release of Ca2+ from the sarcoplasmic reticulum. The potentiation of the second phase by dantrolene and in low Ca2+ solution, was attributed to sodium lauryl sulfate-induced desensitization.