L-glutamate evoked release of GABA from cultured avian retina cells does not require glutamate receptor activation.
gamma-Aminobutyric acid (GABA) and L-glutamate are the major inhibitory and excitatory transmitters in the central nervous system. Recent evidence has indicated that L-glutamate may stimulate GABA release by a novel exchange mechanism (Nascimento and De Mello, J. Neurochem., 1985, 45: 1820-1827). Here we provide strong support for this hypothesis by showing that the L-glutamate-evoked release of [3H]GABA from cultured avian retina cells is not dependent on the activation of excitatory amino acid receptors. Retina cells were found to incorporate [3H]GABA into a pool that was released when cultures were treated with L-glutamate (100 microM). This release was unaffected when calcium ions were removed, but was prevented when NaCl was replaced by LiCl. D-Aspartate, which in tracer experiments was shown to be taken into cells by the same carrier as L-glutamate, was also able to evoke release of [3H]GABA, with the same requirement for NaCl. In addition, L-glutamate and D-aspartate uptake by retina cells was inhibited in more then 80% when the uptake was measured in the presence of LiCl. As opposed to GABA, the release of acetylcholine (ACh) promoted by L-glutamate showed characteristics of classical mechanisms of neurotransmitter release. Glutamate-induced efflux of ACh was Ca2+-dependent and was not affected when NaCl was replaced by LiCl. Also, D-aspartate was ineffective in eliciting the release of ACh. Even at high concentrations, antagonists of excitatory amino acid receptors were unable to diminish the glutamate-evoked release of [3H]GABA.(ABSTRACT TRUNCATED AT 250 WORDS)
D000109:Acetylcholine / Q000378:metabolism; D000818:Animals; D001224:Aspartic Acid / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D002478:Cells, Cultured; D002642:Chick Embryo; D002712:Chlorides / Q000494:pharmacology; D002794:Choline / Q000378:metabolism; D003035:Cobalt / Q000494:pharmacology; D005971:Glutamates / Q000494:pharmacology*; D018698:Glutamic Acid; D007700:Kinetics; D008094:Lithium / Q000494:pharmacology; D018021:Lithium Chloride; D008274:Magnesium / Q000494:pharmacology; D017470:Receptors, Glutamate; D017981:Receptors, Neurotransmitter / Q000502:physiology*; D012160:Retina / Q000187:drug effects / Q000502:physiology*; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D002712:Chlorides; D005971:Glutamates; D017470:Receptors, Glutamate; D017981:Receptors, Neurotransmitter; D001224:Aspartic Acid; D003035:Cobalt; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid; D008094:Lithium; D018021:Lithium Chloride; D008274:Magnesium; D002794:Choline; D000109:Acetylcholine; D002118:Calcium