Release of Calcitonin Gene‐Related Peptide‐Like Immunoreactive Substance from Neuromuscular Junction by Nerve Excitation and Its Action on Striated Muscle

Abstract

In a rat phrenic nerve-hemidiaphragm preparation, calcitonin gene-related peptide (CGRP) increased the twitch contraction induced by nerve or transmural stimulation dose dependently. Either electrical or high K⁺ stimulation of the phrenic nerve caused release of a CGRP-like immunoreactive substance (CGRP-LIS) in a Ca²⁺-dependent manner. Electrical stimulation of the phrenic nerve also increased the cyclic AMP content in diaphragm. This increase was not observed in Ca²⁺-free medium and was blocked by antiserum against CGRP. These results indicate that excitation of the motor nerve causes release of CGRP-LIS at nerve terminals and that the released CGRP-LIS increases the cyclic AMP content of skeletal muscles and potentiates twitch contraction.