title: GTP uptake into rat brain synaptic vesicles.
abstract: Uptake of neurotransmitters into synaptic vesicles is driven by an electrochemical gradient generated by a vacuolar-type proton pump ATPase. This uptake implies a key role for synaptic vesicles in the regulation of neurotransmitter systems. Guanine nucleoside and nucleotides are involved in the inhibition of glutamate-induced cellular responses via an extracellular action and diverse trophic, proliferative, and modulatory effects of guanine nucleotides on neural cells have been shown. Here, we characterized the uptake of GTP into synaptic vesicles isolated from whole rat brain, by using a tritiated poorly-hydrolyzable GTP analog, 5'-guanylylimidodiphosphate ([3H]GppNHp). Uptake of GTP into synaptic vesicles is saturable, time- and temperature-dependent, and relies on a proton-eletrochemical gradient. However, [3H]GMP and [3H]GDP radioactive labeling in synaptic vesicles is not dependent on temperature and vesicular ATPase activity, which indicates that these nucleotides only bind to and are not taken up into synaptic vesicles. GTP is taken up by the same eletrochemical gradient-dependent transport system, as are neurotransmitters storage, which indicates that this guanine nucleotide may also function as a neurotransmitter.
authors.affiliation: Departamento de Bioquímica, Centro de Ciências Biológicas, Universidade Federal de Santa Catarina, Campus Universitário, Trindade, 88040-900 Florianópolis, SC, Brazil.
authors.forename: Tiago G
authors.initials: TG
authors.lastname: Santos
authors.forename: Diogo O
authors.initials: DO
authors.lastname: Souza
authors.forename: Carla I
authors.initials: CI
authors.lastname: Tasca
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D001921:Brain / Q000378:metabolism*; D017301:Ca(2+) Mg(2+)-ATPase / Q000037:antagonists & inhibitors; D003080:Cold Temperature; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018698:Glutamic Acid / Q000494:pharmacology; D006153:Guanosine Diphosphate / Q000378:metabolism; D006157:Guanosine Monophosphate / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000378:metabolism* / Q000494:pharmacology; D006165:Guanylyl Imidodiphosphate / Q000493:pharmacokinetics; D018942:Macrolides / Q000494:pharmacology; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D013572:Synaptic Vesicles / Q000378:metabolism*; D013997:Time Factors
chemical_list: D004791:Enzyme Inhibitors; D018942:Macrolides; D006153:Guanosine Diphosphate; D006165:Guanylyl Imidodiphosphate; D018698:Glutamic Acid; D006157:Guanosine Monophosphate; D006160:Guanosine Triphosphate; C040929:bafilomycin A1; D000255:Adenosine Triphosphate; D017301:Ca(2+) Mg(2+)-ATPase