Interaction between the horizontal cells of the turtle retina]

The interaction between horizontal cells in the turtle retina was tested by means of two microelectrodes, polarizing and recording ones impaling two cells at different distances between each other. The direct electrical coupling is shown to exist between L-cells of the same type (type I - with big receptive fields and type II - with small receptive fields). The value of this coupling changes with the conditions of illumination as well as with the level of the membrane potential. This can be accounted for by the known properties of subsynaptic and nonsynaptic membranes of the horizontal cells. There is no direct electrical coupling between L-cells of different types. However strong hyperpolarization of L-cells of type I by extrinsic current or by a light annulus evokes a depolarization in L-cells of type II. This indirect interaction between L-cells also dependent on the conditions of illumination may be explained by a mechanism of feedback between the horizontal cells and photoreceptors. Polarization of L-cells of both types has no effect on the cells of C-type.