Chemical release of dopamine from striatal homogenates: evidence for an exchange diffusion model
Fischer, J.F.; Cho, A.K.
Journal of Pharmacology and Experimental Therapeutics 208(2): 203-209
1979
ISSN/ISBN: 0022-3565 PMID: 762652 Document Number: 150280
Dopamine and p-hydroxyamphetamine, which is a releasing amine, share a common facilitated diffusion system for uptake into rat striatal homogenates. Transport appears to be by a mobile protein carrier capable of complexing with these substrates and transporting them from 1 side of the synaptosomal membrane to the other in either direction. Uptake of dopamine and releasing amines, and the release of [3H]dopamine induced by these amines in striatal homogenates is: temperature dependent, saturable, stereoselective, sensitive to structural modification of the substrate, sensitive to Na and K concentrations and inhibited by competitive and noncompetitive agents. Chemical release can be explained by an exchange diffusion model with the exchange taking place at the binding site of the uptake carrier. Exchange diffusion is a model in which the movement of 1 substrate into a compartment stimulates the efflux of a 2nd substrate from that compartment. In this system the releasing amines being transported into the synaptosomes down their concentration gradients accelerates the efflux of dopamine out of the synaptosomes, down its concentration gradient, by increasing the probability of exchange. Once the dopamine has been released, the high concentration of the releasing amine outside the synaptosome prevents its reuptake.