[The non-synaptic membrane of the retinal horizontal cells as an amplifier of slow potentials]

A simplified model of the membrane of horizontal cells of L-type is suggested. The model reflects two main features of these cells studied earlier experimentally: 1) their hyperpolarizing response to light results from a decrease in EPSP maintained continuously in the dark; 2) the resistance of nonsynaptic membrane of these cells drops under hyperpolarization within a physiological range (from 0 to 70 mV). The model reproduces such properties of horizontal cells as a low membrane potential in the dark, inversion of the response to light with depolarization above a zero level of the membrane potential, an effect of mutual amplification of colour signals, saturation of the response in the bright light, peculiarities of stationary V-A-characteristics in the dark and in the light, as well as a shape of stationary relations between the membrane potential and light intensity which often have a steep part within a certain range of membrane potentials. The existence of hysteresis loops in V-A-characteristics and relations between the membrane potential and light intensity predicted by the model was confirmed experimentally in horizontal cells of fish retina. The analysis of the model and experimental results show that the nonsynaptic membrane of horizontal cells is able to amplify actively the slow graded potentials.