Dopamine levels of two classes of vesicles are differentially depleted by amphetamine

Differential depletion of neurotransmitter by amphetamine in two classes of vesicles, termed large vesicles and small vesicles, has been studied with amperometry. Carbon fiber microelectrodes have been used to monitor and quantify exocytotic events. Current transients, corresponding to individual exocytotic events, have been obtained from the cell body of the dopamine-containing neuron of Planorbis corneus. The dopamine released from individual vesicles of these cells has been compared for cells treated with D-amphetamine vs. control cells. Our results show that amphetamine has differential effects on the release of dopamine from the two classes of vesicles. Thus, it is concluded that at low concentrations, amphetamine preferentially depletes the large vesicles with a minimal effect on the small vesicles. At high concentrations, amphetamine depletes small vesicles more strongly than large vesicles although amphetamine continues to deplete the large vesicles in a dose-dependent manner. Our data appear to indicate that the two classes of vesicles observed in the Planorbis dopamine neuron might have different mechanisms associated with transmitter depletion.