Abstract
Voltage-clamp methods were employed to study the effects of serotonin (5-HT) and dopamine on the pharmacologically isolated calcium current in the identified Aplysia neuron R15 grown in cell culture. Neurons were obtained from juvenile animals and had not yet developed the bursting pacemaker pattern of activity characteristic of R15 in mature animals. In R15 5-HT elicits a biphasic response consisting of excitatory depolarization followed by an inhibitory hyperpolarization and dopamine elicits an inhibitory hyperpolarization. 5-HT increased the Ca 2+ current without affecting its voltage dependence. The 5-HT effect persisted when Ba 2+ was employed to carry current through Ca 2+ channels. 5-HT did not affect the rate of Ca 2+-dependent Ca 2+ current inactivation other than through its effect on the magnitude of the Ca 2+ current. The adenylate cyclase activator forskolin, in the presence of a phosphodiesterase inhibitor, also increased the magnitude of the Ca 2+ or Ba 2+ current. This result suggested that the 5-HT-induced enhancement of Ca 2+ current was mediated by cAMP. Dopamine inhibited Ca 2+ current when either Ca 2+ or Ba 2+ was employed as the current carrier. Dopamine did not affect the rat of Ca 2+-dependent inactivation of Ca 2+ current other than through its effect on the magnitude of the Ca 2+ current. Intracellular injection of the Ca 2+ chelator EGTA inhibited serotonergic modulation of the Ca 2+ current but not dopaminergic modulation. These results indicated that the putative neurotransmitters 5-HT and dopamine may regulate bursting activity in mature R15 neurons through modulation of Ca 2+ current.
Published Version
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