Modulation of dopamine receptors in the Tapes clam by dextroamphetamine and phenylethanolamine

The mechanism underlying the modulation, by dextroamphetamine and compounds related to phenylethanolamine, of responses to dopamine and serotonin has been studied in the isolated ventricle and aortic bulb of the clam Tapes watlingi. Dextroamphetamine and phenylethanolamine but not cocaine and benztropine have the ability to unmask inhibitory responses to both dopamine and serotonin in the ventricle. Chlordimeform but not clozapine attenuates the inhibitory response to both dextroamphetamine and phenylethanolamine in concentrations which have little or no effect on the inhibitory response to dopamine in the ventricle. Phenylethanolamine, dextroamphetamine, phenylpropylolamine and p-chloro-phenylethanolamine but not octopamine or noradrenaline attenuate the contractile responses to both dopamine and serotonin in preparations of the quiescent aortic bulb. These data show that there are specific receptors for phenylethanolamine in the Tapes heart capable of modulating responses to dopamine and serotonin, and suggests that this biogenic phenethylamine can act as an environmental and physiological factor which may determine how the mollusc heart responds to dopamine.