Effects of locally applied chemicals on transretinal potential and horizontal cells in the isolated carp retina I. Amino acids.

Experiments were performed on isolated retinas of teh carp (Cyprinus carpio) to investigate the effects of locally applied amino acids on the transretinal potential and the membrane potential of horizontal cells. A minute quantity of each solution of an amino acid was applied locally at different layers by means of pressure-microinjection. The responses were induced by alternating central and annular stimuli of white light. Amino acids applied locally at the distal layer (receptor surface or outer plexiform layer) in the centrally stimulated area, caused, at concentrations of 25--50mM, rapid changes in the light-induced potential, whereas those microinjected into the inner plexiform layer did not. When applied locally at the distal layer, amino acids abolished the proximal PIII response and reduced the amplitude of S-potentials, particularly in response to a central stimulus. However, the resting potential of horizontal cells was depolarized only slightly by acidic amino acids. The results suggest that the passive membrane properties of horizontal cells are not altered significantly by the amino acids applied. Differential susceptibilities of the PII component to acidic and neutral amino acids were found; the former did not change or, in some cases, enlarged, whereas the latter abolished it. Possibly, neutral amino acids interfere with a neural mechanism generating the PII component.