Developing skeletal muscle cells express functional muscarinic acetylcholine receptors coupled to different intracellular signaling systems

1 This study analyzed the expression of muscarinic acetylcholine receptors (mAChRs) in the rat cultured skeletal muscle cells and their coupling to G protein, phospholipase C and adenylyl cyclase (AC). 2 Our results showed the presence of a homogeneous population of [H-3]methyl-quinuclidinyl benzilate-binding sites in the membrane fraction from the rat cultured muscle (K-D = 0.4 nM, B-max = 8.9 fmol mg protein(-1)). Specific muscarinic binding sites were also detected in denervated diaphragm muscles from adult rats and in myoblasts isolated from newborn rats. 3 Activation of mAChRs with carbachol induced specific [S-35]GTP gamma S binding to cultured muscle membranes and potentiated the forskolin-dependent stimulation of AC. These effects were totally inhibited by 0.1-1 mu M atropine. 4 In addition, mAChRs were able to stimulate generation of diacylglycerol (DAG) in response to acetylcholine, carbachol or selective mAChR agonist oxotremorine-M. 5 The carbachol-dependent increase in DAG was inhibited in a concentration-dependent manner by mAChR antagonists atropine, pirenzepine and 4-DAMP mustard. 6 Finally, activation of these receptors was correlated with increased synthesis of acetylcholinesterase, via a PKC-dependent pathway. 7 Taken together, these results indicate that expression of mAChRs, coupled to G protein and distinct intracellular signaling systems, is a characteristic of noninnervated skeletal muscle cells and may be responsible for trophic influences of acetylcholine during formation of the neuromuscular synapse.