Nitric oxide enhances amino acid release from immature chick embryo retina

Nitric oxide (NO) was investigated for its ability to induce amino acid release from immature chick retina. The production of endogenous NO by activation of NO synthase after stimulation of N-methyl-D-aspartate (NMDA) subtype of glutamate receptor caused a significant increase in basal release of gamma-aminobutyric acid (GABA) and glutamine, whereas a more modest increase in the glutamate release was also observed. The exposure of chick retina from 9-day-old embryos to NO-generating compounds, S-nitroso-N-acetylpe-nicillamine (SNAP) and sodium nitroprusside (SNP) produced a dose dependent increase in GABA, glutamine, and glutamate release. This effect was reduced by about 80% by haemoglobin. These results indicate that NO has a stimulatory effect on amino acid release from chick embryo immature retina. However, this effect does not appear to involve a cGMP-related mechanism because 8-bromo-cGMP, a stable analogue of cGMP, failed to affect spontaneous amino acid release and because zaprinast did not enhance NMDA-stimulated release. In conclusion, our present observations may account for a role of NMDA-mediated events in the biochemical maturation under depolarizing conditions.