NITRIC-OXIDE ENHANCES AMINO-ACID RELEASE FROM IMMATURE CHICK-EMBRYO RETINA

Nitric oxide (NO) was investigated for its ability to induce amino aci d 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, wherea s a more modest increase in the glutamate release was also observed, T he exposure of chick retina from 9-day-old embryos to NO-generating co mpounds, S-nitroso-N-acetylpenicillamine (SNAP) and sodium nitroprussi de (SNP) produced a dose dependent increase in GABA, glutamine, and gl utamate 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 n ot appear to involve a cGMP-related mechanism because 8-bromo-cGMP, a stable analogue of cGMP, failed to affect spontaneous amino acid relea se and because zaprinast did not enhance NMDA-stimulated release. In c onclusion, our present observations may account for a role of NMDA-med iated events in the biochemical maturation under depolarizing conditio ns.