| Abstract: | Changes in ionic conductance lying at the basis of nonlinearity of the current-voltage characteristic curve of the cell (nonsynaptic) membrane of horizontal cells were studied in experiments on the goldfish and turtle retina. All measurements were made during blocking of synaptic transmission by bright light or Co++. An increase in the K+ concentration led to depolarization and to a reduction of the steepness of the hyperpolarization branch of the current-voltage curve, whereas a decrease in K+ had the opposite effect. Changes in the Cl– or Na+ concentrations had no significant effect on membrane potential or on the shape of the current-voltage curve. The principal potential-forming ion in the horizontal cells is thus K+; conductance for Cl– is absent or very low, and conductance for Na+ also is evidently small. In the presence of Ba++ (2–5 mM) the steepness of the hyperpolarization branch of the current-voltage curve was increased and the whole curve became more linear. It is concluded that nonlinearity of the current-voltage curve of the horizontal cell membrane is due mainly to potential-dependent potassium channels, whose conductance increases during hyperpolarization; this increase in conductance is blocked by Ba++. An increase in the Ca++ concentration to 20 mM led to an increase in steepness of the depolarization branch of the current-voltage curve, suggesting that depolarization increases membrane conductance for Ca++.Institute for Problems in Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 13, No. 5, pp. 531–539, September–October, 1981. |
