Release of gamma-amino[3H]butyric acid from cultured amacrine-like neurons mediated by different excitatory amino acid receptors.
The release of preaccumulated gamma-amino[3H]butyric acid ([3H]GABA) from putative GABAergic amacrine cells was studied in neuronal monolayer cultures made from embryonic chick retina. Release was specifically stimulated by excitatory amino acid agonists. N-Methyl-D-aspartate (NMDA; EC50, 19.1 +/- 5.0 microM), kainic acid (EC50, 15.6 +/- 2.3 microM), and the presumptive endogenous ligand glutamate (EC50, 3.6 +/- 0.5 microM) showed the same efficacy. Quisqualic acid, although the most potent agonist (EC50, 0.56 +/- 0.12 microM), was only half as efficacious. The time course of [3H]GABA release and autoradiographic visualization of responsive GABA-accumulating cells suggest that approximately 50% of the [3H]GABA-accumulating cells possess no or very low responsiveness to quisqualic acid. Depolarization (56 mM KCl)-induced release was fivefold lower than the maximal effect elicited by excitatory amino acids. Release of [3H]GABA and of endogenous GABA was entirely independent of extracellular Ca2+ but was completely abolished after replacement of Na+ by choline or Li+. The effects of NMDA and low concentrations of glutamate (up to 10 microM) were blocked by 2-amino-5-phosphonovaleric acid, by MK 801, and (in a voltage-dependent manner) by Mg2+. The reduction of NMDA responses by kynurenic acid was reversed by D-serine, and quisqualic acid competitively inhibited kainic acid-evoked release. Our results show that the cultured [3H]GABA-accumulating neurons, which probably represent the in vitro counterparts of GABAergic amacrine cells, express at least two types of excitatory amino acid receptors (of the NMDA and non-NMDA type), both of which can mediate a Ca2(+)-independent but Na2(+)-dependent release of GABA.
Hofmann
H D
HD
Department of Neuroanatomy, Max-Planck-Institut für Hirnforschung, Frankfurt, F.R.G.
Möckel
V
V
D000596:Amino Acids / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D001345:Autoradiography; D002118:Calcium / Q000494:pharmacology; D002478:Cells, Cultured; D002642:Chick Embryo; D004305:Dose-Response Relationship, Drug; D007477:Ions; D009474:Neurons / Q000378:metabolism*; D017459:Receptors, Amino Acid; D011956:Receptors, Cell Surface / Q000502:physiology*; D012160:Retina / Q000166:cytology / Q000378:metabolism*; D012964:Sodium / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D000596:Amino Acids; D007477:Ions; D017459:Receptors, Amino Acid; D011956:Receptors, Cell Surface; D005680:gamma-Aminobutyric Acid; D012964:Sodium; D002118:Calcium