The effect of cortisol on the excitability of the rat muscle fibre membrane and neuromuscular transmission
Dlouhá, H.; Vyskocil, F.
Physiologia Bohemoslovaca 28(6): 485-494
1979
ISSN/ISBN: 0369-9463 PMID: 230528 Document Number: 147174
Cortisol when applied in vitro, exerted 2 different effects on the electrical excitability of the diaphragm muscle fiber membrane and on the neuromuscular transmission depending on the concentration used. At low concentrations (2.5 .times. 10-6 M-1) it potentiated action potentials, increased resting membrane polarization by 3-4 mV and did not affect neuromuscular transmission. Higher concentrations (10-2 M-1) suppressed the action potential to a certain extent, depolarized the muscle fiber membrane by 6 mV and reduced the amplitudes of m.e.p.p. [miniature end-plate potentials] and e.p.p. [end-plate potentials] as well as those of iontophoretically evoked acetylcholine potentials. The effect of low concentrations of cortisol is primary and is probably due to the enhancement of resting membrane permeability for K+ ions and to the changes in ion channels. Cortisol in high doses increased muscle oxygen consumption, so that its suppressing effect might be due to inhibition of energy metabolism.