The effects of glycine and GABA on isolated horizontal cells from the salamander retina.

1. Horizontal cells, identified by their morphology, were isolated from the salamander retina and examined in whole cell patch clamp. 2. All cells showed large outward currents activating positive to about -50 mV, and a minority of cells showed fast, tetrodotoxin-suppressible Na+ currents. Slow inward currents that might shape the light responses were never observed. 3. All cells showed conductance increases to both gamma-aminobutyric acid (GABA) and glycine that were completely blocked by bicuculline and strychnine, respectively. No cross-blocking by these antagonists was observed. Partial replacements of Cl- with large, impermeant anions indicated that both GABA- and glycine-evoked currents were carried by Cl- ions. 4. Responses to both GABA and glycine desensitized strongly with time constants of approximately 2 s. 5. Responses to glutamate were not enhanced by glycine. Similarly, responses to GABA were not enhanced by glutamate. 6. GABA-mediated synaptic interactions between horizontal cells may account for the changes in the kinetics of horizontal cell light responses seen when glycine is applied to the intact retina.