GLYCINE STIMULATION OF GLUTAMATE BINDING TO CHICK RETINAL-PIGMENT EPITHELIUM

The effect of glycine (Gly) and taurine (Tau) on the biochemical and p harmacological properties of [H-3]L-glutamate ([H-3] Glu) binding to m embranes from primary cultures of chick retinal pigment epithelium (RP E), as well as from intact tissue during development was studied. Gly and Tau increase B-max of [H-3]Glu binding to a high affinity site (K- B = 300 nM) in membranes from 16 days in vitro (immature) cultures; ad ditionally, Gly discloses a low affinity Glu-binding site (K-B = 970 n M) at this stage. In membranes from 25 days in vitro (mature) cultures , the high affinity site is no longer present and Tau has no effect on Glu-binding; Gly still stimulates binding to the low affinity site by four fold, with an EC(50) = 200 mu M. Pharmacological profile using s pecific excitatory amino acid (EAA) receptor agonists and antagonists suggests that at 16 days in vitro Glu binds preferentially to metabotr opic Glu receptors (mGluRs), and at 25 days in vitro to ionotropic rec eptors different from neuronal ones. The stimulatory effect of Gly and Tau was also observed in intact RPE, and decreased with increasing em bryonic age. Glu binding was also stimulated in membranes from chick r etina, but not in those from rat brain. Results support the possibilit y of EAA participation in several aspects of RPE physiology, including phagocytosis and cell division.