Influence of calcitonin gene-related peptide release on pH-induced mechanical depression in rat atria

Abstract

Rat atria is richly innervated by sensory nerve fibers that release CGRP when stimulated either by capsaicin or acid pH. We studied the physiological relevance of acid pH-induced CGRP release on changes in atrial contractility and relaxation produced by lowering the pH. Isolated atria electrically paced at 2.77 Hz were exposed to a 10-minute period of metabolic acidosis (pH=6.73±0.01, n=28) after: 1) CGRP release induced by capsaicin 0.5 μM; 2) blockage of CGRP release with ruthenium red (RR) 5 μM; 3) no pretreatment; and 4) CGRP receptor blockage with CGRP<SUB>8-37</SUB> 1 μM. Contractility and relaxation were significantly less depressed by acid pH when CGRP release was prevented by RR or CGRP receptor activation was blocked by CGRP<SUB>8-37</SUB>. The results suggest that CGRP release and the activation of CGRP receptors may be physiologically involved in contributing to the depression of contractility and relaxation induced by acid pH in rat atria.