Acetylcholine and carbachol prevent muscle depolarization in denervated rat diaphragm

Muscle fibres of the rat diaphragm kept in a tissue culture medium became depolarized by 8-10 mV within 3 h after denervation. In the presence of carbachol (CB; 5 x 10(-8) M), and acetylcholine (ACh; 5 x 10(-8) M, the post-denervation depolarization was reduced. Both drugs were used in concentrations which mimicked the effect of non-quantal release of ACh. (+)Tubocurarine (TC) and ouabain did not prevent the protective action of CB, indicating that this effect is not mediated through ACh nicotinic receptors or the electrogenic Na+, K+ pump. Addition of Mg2+, verapamil, diltiazem, nifedipine and Cd2+ in concentrations which block Ca2+ entry virtually inhibited the effect of both cholinomimetics. L-Nitroarginine methylester (NAME), an inhibitor of NO synthase, and haemoglobin, an extracellular scavenger of the NO radical, completely eliminated the protective effect of CB on post-denervation depolarization. The retrograde action of NO produced by cholinomimetics on nerve terminals is postulated.