THE CALCITONIN-GENE-RELATED PEPTIDE-INDUCED ACETYLCHOLINESTERASE SYNTHESIS IN CULTURED CHICK MYOTUBES IS MEDIATED BY CYCLIC-AMP

In vertebrate neuromuscular junctions, postsynaptic specialization inc ludes aggregation of acetylcholine receptors (AChRs) and acetylcholine sterase (AChE). The motor nerve provides soluble factors and electrica l activity to achieve this striking localization of AChRs/AChE. Calcit onin gene-related peptide (CGRP), a neuropeptide synthesized by motor neurons, is able to stimulate the expression of AChR in cultured myotu bes. Similar to AChR regulation, synthesis of AChE in cultured chick m yotubes is also stimulated by CGRP. Application of CGRP onto cultured myotubes stimulated the accumulation of intracellular cyclic AMP (cAMP ) as well as the expression of AChE mRNA and protein. However, the enz ymatic activity of AChE remained unchanged. In cultured myotubes, vari ous drugs affecting the intracellular level of cAMP, such as N-6,O-2-d ibutyryladenosine 3',5'-cyclic monophosphate, cholera toxin, and forsk olin, could mimic the effect of CGRP in stimulating the expression of AChE. When myotubes were transfected with cDNA encoding constitutively active mutant G alpha(s) the intracellular cAMP synthesis was increas ed, The increase in cAMP level was in parallel with an increase in the expression of AChE, whereas transfection of active mutant G alpha(i) cDNA decreased the cAMP level as well as the AChE expression. In addit ion, expression of collagen-tailed AChE was up-regulated by the cAMP p athway. These findings indicated that CGRP-induced AChE regulation is mediated by the cAMP pathway and represented the first evidence to sug gest that the regulation of mRNA synthesis of AChR and AChE can be med iated by the same neuron-derived factor.