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Studies of excitable membranes. III. Freeze-fracture examination of the membrane specializations at the neuromuscular junction and in the non-junctional sarcolemma after denervation

1977; Elsevier BV; Volume: 137; Issue: 2 Linguagem: Inglês

10.1016/0006-8993(77)90333-x

1872-6240

Mark H. Ellisman, John E. Rash,

Ion channel regulation and function

We have examined the effects of denervation upon endplate and non-endplate regions of muscle membrane visualized by freeze-fracture electron microscopy. The rows of putative acetylcholine (ACh) receptor complexes at the tops of functional folds were studied after nerve section. Denervation of up to eight days does not result in a measurable decrease in the packing density of putative receptor particles in regions where they appear to be maintained in rows. However, the rows of particles are not as prominant at the tops of some folds, and in limited regions the rows are reduced or absent. It appears that the effects of denervation, although pronounced in terms of ACh receptors in non-synaptic membrane, are not sufficient to produce large alterations in receptor organization in junctional folds. In addition to the endplate we studied the non-junctional sarcolemmas from both fast twitch extensor digitorum longus (EDL) and slow twitch soleus in order to determine if denervation resulted in systematic changes in the number of rectilinear arrays in fibers from either type of muscle. There was no appearance of rectilinear arrays noticeable in soleus or a disappearance of them in EDL following denervation. Based on the failure of rectilinear arrays to appear in soleus sarcolemmas following denervation and the appearance of similar arrays in cell membranes not involved in ACh receptivity, we conclude that their function is something other than that of the extrajunctional ACh receptor.