title: Evidence for two mechanisms of amino acid osmolyte release from hippocampal slices.
abstract: A 30% decrease in osmolarity stimulated 3H-taurine, 3H-GABA and glutamate (followed as 3H-D-aspartate) efflux from rat hippocampal slices. 3H-taurine efflux was activated rapidly but inactivated slowly. It was decreased markedly by 100 microM 5-nitro-(3-phenylpropylamino)benzoic acid (NPPB) and 600 microM niflumic acid and inhibited strongly by tyrphostins AG18, AG879 and AG112 (25-100 microM), suggesting a tyrosine kinase-mediated mechanism. Hyposmolarity activated the mitogen-activated protein kinases (MAPK) extracellular-signal-related kinase-1/2 (ERK1/ERK2) and p38, but blockade of this reaction did not affect 3H-taurine efflux. Hyposmosis also activated phosphatidylinositide 3-kinase (PI3K) and its prevention by wortmannin (100 nM) essentially abolished 3H-taurine efflux. 3H-taurine efflux was insensitive to the protein kinase C (PKC) blocker chelerythrine (2.5 microM) or to cytochalasin E (3 microM). The release of 3H-GABA and 3H-D-aspartate occurred by a different mechanism, characterized by rapid activation and inactivation, insensitivity to NPPB, niflumic acid, tyrphostins or wortmannin. 3H-GABA and 3H-D-aspartate efflux was not due to external [NaCl] decrease, cytosolic Ca2+ increase or depolarization, or to reverse operation of the carrier. This novel mechanism of amino acid release may be mediated by Ca2+-independent exocytosis and modulated by PKC and actin cytoskeleton disruption, as suggested by its inhibition by chelerythrine and potentiation by 100 nM phorbol-12-myristate-13 acetate (PMA) and cytochalasin E. GABA and glutamate osmosensitive efflux may explain the hyposmolarity-elicited increase in amplitude of inhibitory and excitatory postsynaptic potentials in hippocampal slices as well as the hyperexcitability associated with hyponatraemia.
authors.affiliation: Department of Biophysics, Institute of Cell Physiology, National University of Mexico, Apartado Postal 70-253, 04510 México DF, Mexico.
authors.forename: R
authors.initials: R
authors.lastname: Franco
authors.forename: M E
authors.initials: ME
authors.lastname: Torres-Márquez
authors.forename: H
authors.initials: H
authors.lastname: Pasantes-Morales
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000730:Androstadienes / Q000494:pharmacology; D020533:Angiogenesis Inhibitors / Q000494:pharmacology; D000818:Animals; D001224:Aspartic Acid / Q000737:chemistry / Q000378:metabolism; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology; D003572:Cytochalasins / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D018698:Glutamic Acid / Q000737:chemistry / Q000378:metabolism*; D006624:Hippocampus / Q000187:drug effects / Q000378:metabolism*; D007093:Imidazoles / Q000494:pharmacology; D066298:In Vitro Techniques; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009544:Niflumic Acid / Q000494:pharmacology; D009579:Nitrobenzoates / Q000494:pharmacology; D009994:Osmolar Concentration; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D011725:Pyridines / Q000494:pharmacology; D051381:Rats; D013654:Taurine / Q000737:chemistry / Q000378:metabolism*; D014316:Tritium / Q000737:chemistry / Q000378:metabolism; D020032:Tyrphostins / Q000494:pharmacology; D000077191:Wortmannin; D005680:gamma-Aminobutyric Acid / Q000737:chemistry / Q000378:metabolism*
chemical_list: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D000730:Androstadienes; D020533:Angiogenesis Inhibitors; D001224:Aspartic Acid; D016861:Cyclooxygenase Inhibitors; D003572:Cytochalasins; D004791:Enzyme Inhibitors; D005419:Flavonoids; D018698:Glutamic Acid; D007093:Imidazoles; D020928:Mitogen-Activated Protein Kinases; D009544:Niflumic Acid; D009579:Nitrobenzoates; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011493:Protein Kinase C; D011725:Pyridines; D013654:Taurine; D014316:Tritium; D020032:Tyrphostins; D000077191:Wortmannin; D005680:gamma-Aminobutyric Acid; C007215:cytochalasin E; C058176:5-nitro-2-(3-phenylpropylamino)benzoic acid; C090942:4-(4-fluorophenyl)-2-(4-hydroxyphenyl)-5-(4-pyridyl)imidazole; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one