Permeability changes induced by L-glutamate in solitary retinal horizontal cells isolated from Carassius auratus.

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Abstract
Solitary horizontal cells isolated from goldfish retinae are depolarized by L-glutamate (Glu), a possible candidate for the transmitter of photoreceptors. The underlying mechanisms were analyzed under voltage-clamp conditions using giga-seal suction pipettes in the whole-cell recording configuration. Glu induced an inward current at the resting membrane potential (.apprx. -57 mV). Membrane depolarization decreased the amplitude of Glu-induced current and reversed its polarity to outward beyond .apprx. -3 mV. Membrane hyperpolarization below the resting potential decreased the amplitude of the Glu-induced inward current. When a K current through the anomalous rectifier, which is activated by membrane hyperpolarization, was blocked by Cs ions, the phenomenon disappeared and the Glu-induced current increased in amplitude with hyperpolarization. Mg ions had no effect on the reduction of the Glu-induced current at hyperpolarized potentials. Glu probably produced 2 types of conductance change: a conductance increase due to an activation of Glu channels and a conductance decrease due to a blockage of the K current through the anomalous rectifier. The Glu-activated channel was permeable to cations with low selectivity, but not to anions. The least effective dose of Glu was < 10 .mu.M. The relation between the Glu-induced current and the membrane potential curved upwards near the reversal potential, and this relation was not affected by Mg ions.