Characterization of the gubernacular contractile response to calcitonin gene-related peptide in the mouse

Abstract

Calcitonin gene-related peptide (CGRP) has no effect on quiescent skeletal muscle, but cultured neonatal mice gubernacula show rhythmic contractions in response to CGRP. This study investigated whether these contractions (1) require calcium ions, (2) are activated via acetylcholine receptors, or (3) require dihydropyridine receptors. Gubernacula (n = 20 for each experiment) from male mice aged 7 days old were preincubated for 30 minutes in aerated culture medium (Krebs-Henseleit solution) with (1) up to 1.8 mmol/L of calcium with or without CGRP (714 nmol/L), (2) up to 5.0 μmol/L of curare with CGRP and calcium (1.8 mmol/L), or (3) up to 1 μmol/L of nifedipine with CGRP and calcium. Then they were placed on agar-coated grids over the same compound solutions, and observed for 2 days by video camera to see contractions. Of gubernacula cultured with calcium (1.8 mmol/L) and CGRP, 90% showed contractions, which decreased to 20% without CGRP ( P < .001) and 15% without calcium ( P < .001). Only 5% of gubernacula cultured without both CGRP and calcium showed contractions. Also these contractions in response to CGRP depended on calcium concentrations in a dose-dependent manner. Curare did not suppress contractions. With increasing dose of nifedipine, the percentage of gubernacula contracting decreased from 95% to 0%. These results suggest that developing mouse gubernacular contractions in response to CGRP require influx of calcium ions to the sarcoplasm via dihydropyridine receptors in a similar manner to contractions of immature cardiac or smooth muscles, and these contractions are not activated via acetylcholine receptors.