Electrical and morphological properties of off-center bipolar cells in the carp retina

Electrical membrane properties of carp off-center bipolar cells were studied by injecting a ramp of current (changing at a rate of about 0.3 nA/s) through one barrel of a double-barreled electrode and recording the voltage drop through the other barrel. The light-elicited response reversed the polarity at a positive membrane potential. The current-voltage curve showed inward and outward rectifications which modified the amplitude of the light-elicited response. The degree of membrane rectifications varied considerably among the cells sampled. Off-center bipolar cells were stained by iontophoretic injections of Lucifer-yellow dye after studying their electrical properties. There was a significant correlation between the difference in cell morphology and the degree of membrane rectification. The cells, which were characterized by small cell bodies lying close to the proximal part of the inner nuclear layer and by thin primary dendrites, tended to show rectifying membrane properties, compared to those characterized by large cell bodies lying close to the distal part of the inner nuclear layer and by thick primary dendrites. A site showing rectifying membrane properties and the origins of a large variability in membrane rectifications are discussed in detail.