Physiological effects of carbamylcholine, cyclic GMP and related agents on isolated rat ventricular myocytes

The purpose of the present investigation was to ascertain the sensitivity of single dissociated myocardial cells to carbamylcholine and related substances. Heart cell cultures were obtained from newborn rat ventricles. The contractile activity was monitored by using a photoelectric transducer. The present results indicate that carbamylcholine alone or in association with sympathomimetic agents, i.e. isoproterenol, dibutyryl cyclic AMP and isobutylmethylxanthine, had no effect on the beating rate of the cultured ventricular cells. Moreover, dibutyryl cyclic GMP did not counteract the chronotropic response induced by either isoproterenol or dibutyryl cyclic AMP. Our findings failed thus to demonstrate the existence of activable muscarinic receptors in ventricular myocytes cultivated from the newborn rat and therefore supports the idea that the interaction between the adrenergic tone and the vagal innervation in the mammalian ventricle should be presynaptic. Furthermore, the present results seem to rule out the possibility of a mutual antagonism between cyclic AMP and cyclic GMP in this preparation.