Ionic mechanism for the generation of horizontal cell potentials in isolated axolotl retina.

Abstract

The ionic mechanism of horizontal cell potentials was investigated in the isolated retina of the axolotl Ambystoma mexicanum. The membrane potentials of receptors and horizontal cells were recorded intracellularly, while the ionic composition of the medium flowing over the receptor side of the retina was changed. The membrane potential of the horizontal cell was highly dependent on the extracellular concentration of Na+. When the external ion concentration of either Cl- or K+ was changed independently of the other, there were shifts in the membrane potential of the horizontal cell which could not be explained by changes in the equilibrium potential of these ions. If the external concentrations of K+ and Cl- were varied so that the product of their external concentrations did not change, the shift in the membrane potential of the horizontal cell was in the direction predicted by the Nernst equation. Apparently in the dark the receptors release a synaptic transmitter which increases primarily the Na+ conductance of the horizontal cell postsynaptic membrane.