Solitary horizontal cells in culture--II. A new tool for examining effects of photoreceptor neurotransmitter candidates.

Membrane potentials of solitary horizontal cells dissociated from goldfish retinas were intracellularly measured while applying various acidic amino acids. L-glutamate and kainic acid depolarized solitary horizontal cells at micromolar doses. Neither L- nor D-aspartate produced any change in solitary horizontal cell resting potentials. Low-amplitude responses to L-glutamate showed no sign of desensitization. A steady, plateau-like, dose-dependent component of solitary horizontal cell responses to either L-glutamate or kainic acid, though obscured during its rising phase by action potentials, was always recorded during maintained agonist applications. Responses to either L-glutamate or kainic acid reversed in polarity at membrane potentials between 0 and -20 mV. Responses to L-glutamate collapsed reversibly when extracellular sodium ions were replaced by choline ions. Responses to either L-glutamate or kainic acid were antagonized by relatively high doses of D-aspartate. These results demonstrate that retinal horizontal cell chemosensitivity to acidic amino acids persists after dissociation, and in several respects resembles that found in several other preparations, including retinas in situ.