Amino acids as osmolytes in the retina

Amino acids play a role as osmolytes during the regulatory volume decrease subsequent to hyposmotic swelling, but less is known about its role when sw elling occurs in isosmotic conditions. In this work we examined the efflux of labelled GABA, taurine and glutamate (traced as D-aspartate) from the ch ick retina, after isosmotic swelling evoked by KCl-containing solutions, an d compared its features to those in hyposmotic swelling. In both conditions , GABA and taurine efflux were more sensitive to swelling than glutamate, a s assessed by the activation threshold and the amount released. The amino a cid efflux in hyposmotic media was decreased by DIDS, tamoxifen and NPPB, a gents acting as Cl channels blockers, which also inhibit the osmosensitive Cl efflux. The component associated with swelling in the KCl-stimulated eff lux was assessed by the reduction observed when Cl is replaced by an imperm eant anion, or by the influence of hyperosmotic media. GABA and taurine eff lux exhibited a large swelling-dependent component, which was lower for D-a spartate. This component was markedly decreased by NPPB, but this was due t o an effect of the blocker preventing swelling. These results suggest that the influx of Cl, acting as K counterion, which is responsible for cell swe lling, occurs through a pathway sensitive to NPPB, similarly to that activa ted by hyposmolarity. This finding may be of interest in studies aiming at preventing the cell edema which occurs in a number of pathologies.