Dopamine uptake during fast-phase endogenous dopamine release from mouse striatal synaptosomes.

[3H]Dopamine (DA) uptake and endogenous DA release were measured in mouse striatal P2 synaptosomes over a 1 30-s period in the presence and absence of KCl depolarization. Approximately 70% of the total DA release over the 30-s period occurred within the first 5 s of depolarization. [3H]DA uptake over this same period was less than 5% of the corresponding release value. The magnitudes and rates of uptake were moderately inhibited by 30 mM KCl depolarization. These decreases were not fully explained by the reduction in sodium present during depolarization or by the dilution of labelled DA by released endogenous DA. Non-linear regression analysis of the uptake data revealed fast (less than 1 s) and slow (greater than 1 s) components of uptake which were differentially affected by KCl depolarization. The results of this study indicate the presence of a rapid, multi-component synaptosomal DA uptake process which appears to play a small role in regulating in vitro endogenous DA release during the initial seconds of KCl depolarization. If synaptosomal uptake reflects the in vivo situation, presynaptic neuronal uptake may be more important in the long-term regulation of transmitter release by maintaining intracellular dopamine storage pools which are linked to synthesis and release processes.