PRESENCE OF THE BINDING OF A VARIETY OF LIGANDS RELATED TO IONOTROPIC EXCITATORY AMINO-ACID RECEPTORS IN RAT RETINA

The binding of [H-3]L-glutamic (Glu), [H-3](+/-)-3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic and [H-3]D,L-(E)-2-amino-4-propyl-5-phosphono-3-pentenoic acids was detected in rat retinal membranes extensively washed and treated with a low concentration of Triton X-100, in addition to the binding of both [H-3]glycine (Gly) and [H-3]5,7-dichlorokynurenic acid. Furthermore, retinal membranes exhibited the binding of [H-3](+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine in the presence of Glu, Gly and spermidine irrespective of the incubation period employed. Rat retina also contained the binding of [H-3]kainic acid as well as the binding of [H-3]alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid which was sensitive to potentiation by potassium thiocyanate. In addition, the binding of both [H-3](+)-3-(hydroxyphenyl)-N-(l-propyl)piperidine and [H-3]1,3-di-o-tolyl-guanidine was found in rat retinal membranes extensively washed but not treated with Triton X-100. These results give support for the proposal that the rodent retina contains subclasses of ionotropic brain excitatory amino acid receptors including the N-methyl-D-aspartate receptor ionophore complex as well as sigma sites.