title: Interaction between dopamine influx and efflux in rat striatal synaptosomes.
abstract: Exchange release has previously been proposed as the mechanism by which dopamine is transported over the synaptosomal membrane. An increase in carrier-mediated dopamine release should therefore result in an enhanced rate of synaptosomal dopamine uptake. In order to test this hypothesis, rat striatal synaptosomes were incubated with 14C-dopamine until equilibrium. Then, the 14C-dopamine concentration in the medium was reduced in order to elicit various rates of net dopamine efflux, while influx was monitored using tracer amounts of 3H-dopamine. Dopamine release was concentration dependent and saturable and thus may be carrier-mediated. In contrast to that expected for a mechanism of exchange release, dopamine influx was depressed as compared to equilibrium conditions. Furthermore, nomifensine, a specific inhibitor of dopamine influx, did not attenuate dopamine efflux. It is concluded that dopamine transport over the synaptosomal membrane may not be via a mechanism of strict exchange release.
mesh_terms: D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D003342:Corpus Striatum / Q000378:metabolism*; D004298:Dopamine / Q000378:metabolism*; D008297:Male; D009627:Nomifensine / Q000494:pharmacology; D051381:Rats; D013574:Synaptosomes / Q000378:metabolism*
chemical_list: D009627:Nomifensine; D004298:Dopamine