Differential effects of succinylcholine and acetylcholine on endplate and extrajunctional membranes of normal and denervated mouse skeletal muscle fibres.

Depolarization provoked by 10(-7)-10(-4) succinylcholine (SCh) and acetylcholine (ACh) was measured in thin bundles dissected from normal and 1-15 days denervated mouse muscles using the microelectrode technique. The muscles were superfused by Cl- -free solutions containing 30 mM K+ to prevent contracture responses. In endplate areas of normal muscles, sensitivity to SCh was roughly 10 times higher than the sensitivity to ACh. By contrast, the extrajunctional membrane of chronically denervated muscles was less sensitive to SCh than to ACh by about the same factor. The extrajunctional membrane of non-denervated soleus muscles was also more sensitive to ACh than to SCh but, unlike the response of the denervated membrane, the depolarization was transient.