Calcium Movements in CGRP-treated Cultured Skeletal Muscle Cells: Is There a Role for CGRP in Tension Headaches?

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It was previously determined that the site of action of calcitonin gene-related peptide (CGRP) in cardiomyocytes was predominantly at the sarcolemmal calcium release channel, and studies have shown that CGRP has major effects on intracellular cardiomyocyte calcium concentrations. We postulated that CGRP would have similar effects on striated skeletal muscle and determined the effects of CGRP on calcium levels in cultured chick myotubes by fluorescence imaging. Myoblasts were cultured until they were continuous myotubes. Deconvolution fluorescence imaging was employed to visualize subcellular organelles and construct 3D renditions. Myotubes were treated with a high (1 μM) and a low (1 nM) concentration of CGRP for 1 h or 24 h time periods, and real-time fluorescence spectrophotometry with a calcium specific fluoroprobe permitted the acquisition of images and calcium transients. Experiments also used CGRP 8–37 to ensure specificity of action of the full-length neuropeptide. CGRP localizations by image stacking were made using fluorescence deconvolution microscopy and distributions on the myotubes were shown. Myotube contractions and intracellular calcium levels were dose dependent, a high CGRP concentration producing calcium overload. CGRP 8–37 had no effect on contractions or calcium levels. Reconstructed images revealed the neuropeptide to be localized to juxta-nuclear areas, supporting the likelihood of site specific actions. CGRP has dramatic effects on intracellular calcium in striated muscle, high concentrations producing sustained contractions and calcium overload. The results give support to a mechanistic role for CGRP in muscle tension headaches, and underscore the importance in the development of CGRP analogues or receptor antagonists for treatment.

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