Two pharmacological classes of quisqualate-induced electrical responses in rat retinal ganglion cells in vitro

Abstract

The pharmacological properties of steady state responses elicited by the excitatory amino acid agonists quisqualate and alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) have been examined in isolated rat retinal ganglion cells with patch electrodes. Based upon testing retinal ganglion cells with both agonists at saturating concentrations (30 microM for quisqualate and 60 microM for AMPA), these neurons can be grouped into three different categories: (a) type I cells, in which AMPA steady state responses were larger than those induced by quisqualate; (b) type II cells, in which quisqualate steady state responses were larger than or equal to those produced by AMPA; and (c) type III cells, in which neither AMPA nor quisqualate elicited responses. Regardless of cell type (I or II), AMPA responses were substantially inhibited by the antagonists kynurenate (750 microM) and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX; 10 microM). In contrast, the effects of these antagonists on quisqualate responses varied depending on the cell type, with both kynurenate and CNQX being more effective in type II than in type I cells. Based upon further pharmacological manipulations, it is proposed that quisqualate-induced steady state responses in retinal ganglion cells are divisible into two pharmacological classes that exist in varying proportions in these cells in vitro.