Effect of calcitonin gene-related peptide on skeletal muscle via specific binding site and G protein

In curarized rat skeletal muscle, rat calcitonin gene-related peptide (CGRP), a peptide coexisted with acetylcholine in the motor nerve terminal, increased the isometric twitch force, accompanied by an increase in the active state intensity of shortening, prolonged duration of the active state and additive effect of a phosphodiesterase inhibitor; the results reflect a potentiation in the sarcoplasmic calcium transport system. This CGRP effect was enhanced by cholera toxin, suggesting the activation of guanine nucleotide binding regulatory protein (G protein) that stimulates adenylate cyclase (Gs). The pertussis toxin (IAP), a factor to prevent the cyclic AMP decrease by inactivating the G protein that inhibits adenylate cyclase (Gi), provided no effect on the action of CGRP. The existence of CGRP binding site in the sarcolemmal membrane was confirmed by Scatchard analysis of binding data; affinity of the binding site for CGRP was decreased in the presence of guanosine-5'-[gamma-thio]triphosphate (GTP gamma S). The Gs protein is thus implicated in the CGRP binding site and intracellular processes of signal transduction. CGRP did not modify the neuromuscular transmission and cable properties of the muscle membrane.