THE EXCITATORY AND INHIBITORY AMINO-ACID RECEPTORS ON HORIZONTAL CELLS ISOLATED FROM THE WHITE PERCH RETINA

1. The distribution and the properties of receptors to the inhibitory amino acid glycine (GLY) and the excitatory amino acid glutamate (GLU) and its analogues kainate (KA), quisqualate (QUIS), lpha-amino-3-hydr oxy-5-methyl-4-isoxazolepropionic acid (AMPA), and N-methyl-D-aspartat e (NMDA), were studied with whole-cell and outside-out patch-clamp tec hniques on all four types of horizontal cells isolated from the retina of white perch. 2. Glycine at concentrations above 30 muM evoked whol e-cell current responses from two types of horizontal cells (H2 and H4 ). The other two types of horizontal cells (H1 and H3) were unresponsi ve to GLY (30 muM-3 mM). 3. Responses elicited by GLY from H2 and H4 c ells were similar, consisting of inward currents that desensitized wit h a half-decay time of 0.5-2 s at glycine concentrations between 100 a nd 500 AM. GLY-activated currents were inhibited by the glycine recept or antagonist strychnine (STRYCH). Current responses evoked by GLY rev ersed at the Cl- equilibrium potential. 4. Dose-response analysis of p eak currents induced by GLY revealed a Hill coefficient of 2.0 +/- 0.1 (mean +/- SD, n = 3) and an median effective concentration (EC50) of 85 +/- 2 muM (n = 3). 5. Single glycine receptor channels recorded fro m outside-out patches had a main-state conductance of 47 +/- 4 pS (n = 3). 6. Every type of horizontal cell from the white perch responded t o GLU, KA, QUIS, and AMPA but none responded to exogenously applied NM DA (200 muM) or NMDA (200 muM) + GLY (1 muM) in a Mg+2-free bathing so lution. 7. The ratio of the amplitude of responses to GLU, KA, QUIS, a nd AMPA remained nearly constant among all the horizontal cells tested , suggesting there might be only a single population of non-NMDA recep tors on these cells. 8. QUIS and KA both elicited responses from the h orizontal cells. When applied together with KA, QUIS competitively ant agonized the responses of horizontal cells to KA. 9. The results demon strated the existence of an inhomogeneous distribution of strychnine-s ensitive glycine receptors and a homogeneous distribution of non-NMDA type glutamate receptors among the four types of white perch horizonta l cells.