High-affinity binding ofl-glutamate to chick retinal membranes

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Abstract
Binding ofl-[3H]glutamate to membranes from whole chick retina and from subcellular fractions enriched with photoreceptor terminals (P1), or terminals from the inner plexiform layer (P2) was studied. Na+-dependent and Na+-independent binding to these membranes was demonstrated. Na+-independent binding was stereospecific. Kinetic analysis of the binding process indicated a single high-affinity system (KB=0.55 μM) with a capacity of approximately 20 pmoles/mg protein in all the membrane fractions. [3H]Glutamate binding to P1 and P2 fractions was effectively displaced by several structural analogues of glutamate. Glutamate diethyl-ester appreciably displaced binding, whereas kainic acid did not displace bound glutamate. Data indicate the binding of [3H]glutamate to physiologically relevant receptors in the chick retina.