Stimulation and homologous desensitization of calcitonin gene-related peptide receptors in cultured beating rat heart cells

Abstract

Addition of calcitonin gene-related peptide (CGRP), 1 X 10(-7) M, to cultured neonatal rat heart cells resulted in rapid increases in beating rate and cellular concentrations of cAMP. Calcitonin (1 X 10(-7) M), in contrast, had no significant effect on heart cell beating rate or cAMP content. CGRP-stimulated increases in heart cell cAMP content were rapid, transient, dose dependent, and potentiated by isobutyl-methylxanthine (1 X 10(-4) M). Half-maximal increases in heart cell cAMP content occurred at 1 X 10(-8) M CGRP. Heart cell adenylate cyclase responses to CGRP were desensitized in a rapid (i.e. within 5 min) and dose-dependent manner by prior exposure to CGRP. Complete and half-maximal desensitization of heart cells to CGRP occurred at 1 X 10(-8) and 3 X 10(-10) M CGRP, respectively. Desensitization of heart cells to CGRP did not modify the cAMP response of heart cells to beta-adrenergic agonist stimulation, and beta-adrenergic agonist desensitization of heart cells did not modify responses to CGRP. Heart cell cAMP responses to CGRP were additive to those of the beta-adrenergic agonist isoproterenol and occurred in the presence of beta-adrenergic blockade. These observations demonstrate that CGRP exerts specific and potent agonist actions in cardiac myocytes and that regulation of myocardial responses to CGRP may occur by mechanisms involving increases in cAMP and receptor desensitization.