Exogenous glutamate and taurine exert differential actions on light-induced release of two endogenous amino acids in isolated rat retina

A dark‐adapted isolated rat retina, preloaded with [14C]glutamate ([14C]Glu) and [3H]taurine ([3H]Tau), was superfused with artificial cerebrospinal fluid (ACSF) in the absence and presence of Glu (1 mM) or Tau (1 mM), as well as the Glu uptake inhibitors dihydrokainic acid (DHK, 0.04 mM) and trans‐L‐pyrrolidine‐2,4‐dicarboxylate (t‐PDC, 0.004 mM). After 10 min of light stimulation, the extracellular level of [14C]Glu and [3H]Tau was reduced to 82 ± 2% and 65 ± 4% of the control, respectively. Basal release was enhanced when Tau and t‐PDC were applied together, although none of the compounds had any effect when applied individually. Glu and DHK had no effect. The decrease of [14C]Glu efflux evoked by light stimuli was enhanced by t‐PDC and Tau, either added separately or together, whereas Glu and DHK were without effect. In contrast, [3H]Tau efflux variations induced by light stimuli were reduced markedly by both Tau and Glu. These findings suggest distinctly different roles of Tau and Glu in light‐induced responses in mammalian retina, including a possible role for Tau in light adaptation processes. © 2003 Wiley‐Liss, Inc.