Evidence for two independent mechanisms of GABA release induced by veratridine and glutamate in monolayer cultures of chick embryo retinal cells.
GABA is a major inhibitory neurotransmitter in the central nervous system, including the retina. In the present paper we present evidence for the existence of two independent mechanisms for GABA release in cultured retina cells. Eight-day-old chick embryo retinas were dissociated and plated in 35-mm plastic dishes and cultured for 3 or 7 days at 37 degrees C. An increase of 3 to 5-fold in GABA release was observed in cultures of 3 or 7 days in vitro preloaded with 0.5 microCi [3H]GABA and stimulated with glutamate (100 microM) or veratridine (100 microM). Tetrodotoxin (1 microM) blocked the release induced by veratridine but not by glutamate. In contrast, the non-N-methyl-D-aspartate (NMDA) glutamate antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 100 microM) was able to inhibit GABA release promoted by glutamate but not by veratridine. These results indicate that depolarization of retinal cells by opening of voltage-dependent sodium channels or activation of non-NMDA glutamate receptors can trigger intracellular events that lead to calcium-independent GABA release.
Departamento de Neurobiologia, Universidade Federal Fluminense, Niterói, RJ, Brasil.
J L
JL
do-Nascimento
A L
AL
Ventura
R
R
Paes-de-Carvalho
D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D000818:Animals; D002478:Cells, Cultured; D002642:Chick Embryo; D018756:GABA Antagonists; D005971:Glutamates / Q000494:pharmacology*; D018698:Glutamic Acid; D018377:Neurotransmitter Agents / Q000494:pharmacology*; D011810:Quinoxalines / Q000494:pharmacology; D012160:Retina / Q000166:cytology*; D013779:Tetrodotoxin / Q000494:pharmacology; D014701:Veratridine / Q000494:pharmacology*; D005680:gamma-Aminobutyric Acid / Q000187:drug effects / Q000493:pharmacokinetics*
D018756:GABA Antagonists; D005971:Glutamates; D018377:Neurotransmitter Agents; D011810:Quinoxalines; D018698:Glutamic Acid; D013779:Tetrodotoxin; D005680:gamma-Aminobutyric Acid; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D014701:Veratridine