title: Modulation of dopamine uptake and release in rat striatal synaptosomes by glycine and glutamate.
abstract: The uptake and release of dopamine (DA) by rat brain striatal synaptosomes were studied in presence of glycine or glutamate (0.5-20 mM) in incubation media containing 5 or 55 mM KCl. In low K+ medium glycine, up to 5 mM had little effect on DA uptake, but higher concentrations of the amino acid inhibited the uptake. High K+ medium resulted in a decrease in DA uptake as compared to that of basal K+ medium. Glycine at 1 microM, but not at higher concentrations, prevented the inhibition induced by high K+ depolarization. However, glutamate in the low K+ medium and at a 0.5 mM concentration, stimulated DA uptake, but at higher concentrations it inhibited the uptake. In the high K+ medium, glutamate in all concentrations potentiated the inhibition of DA uptake induced by K+ depolarization. The DA release response of the synaptosomes to glycine concentrations (1-20 mM) in low K+ medium was a biphasic pattern, with a stimulation at 1 mM and an inhibition at higher concentrations. This pattern was reversed when DA release was measured in the high K+ medium. The pattern of DA release in the presence of glutamate concentrations (1-20 mM) was a triphasic one, with an inhibition at 1 mM, stimulation at 5 mM, and a less effective inhibition at higher concentrations. In the high K+ medium, glutamate at 1 mM concentration prevented the stimulation induced by K+ depolarization, but at 5 mM reversed the rate of release to the depolarization state. Results of this study suggest that glycine and glutamate have more than a simple inhibitory or excitatory transmitter role in the striatum, respectively. The identical effects of glycine with that of glutamate in certain concentrations is consistent with previous reports that glycine and N-methyl-D-aspartate (NMDA) act as coagonists of a common excitatory amino acid receptor.
authors.affiliation: Department of Biochemistgry Faculty of Pharmacy, Isfahan Medical Sciences University, Iran.
authors.forename: M
authors.initials: M
authors.lastname: Messripour
authors.forename: Z
authors.initials: Z
authors.lastname: Ali-Babaie
mesh_terms: D000818:Animals; D003342:Corpus Striatum / Q000378:metabolism*; D004298:Dopamine / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D018698:Glutamic Acid / Q000494:pharmacology*; D005998:Glycine / Q000494:pharmacology*; D008297:Male; D018377:Neurotransmitter Agents; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism*
chemical_list: D018377:Neurotransmitter Agents; D018698:Glutamic Acid; D011188:Potassium; D005998:Glycine; D004298:Dopamine