Ionic mechanisms of two types of on-center bipolar cells in the carp retina. I. The responses to central illumination.

Abstract

A B $ T R A C T Properties of the depolarizing response of on-center bipolar cells to a light spot stimulus were studied in the carp retina. On-center bipolar cells were classified into two types, cone-dominant and rod-dominant, according to their major input from cones and rods. Cone-dominant bipolar cells responded to spectral light with the maximum amplitude near 625 nm, suggesting major input from red cones. The response was accompanied by a resistance increase and showed a reversal potential at -63 -+ 21 mV when the membrane was hyperpolarized by current. The results suggest that the photoresponse of cone-dominant cells is due to a decrease of gK and/or gc~, membrane conductances to potassium and chloride, respectively. Rod-dominant bipolar cells responded to spectral light with the maximum amplitude near 525 nm under scotopic conditions and near 625 nm under photopic conditions, providing evidence that they receive input from rods and red cones. In the scoptopic condition their response was accompanied by a resistance decrease and showed a reversal potential at 29 -+ 13 mV, whereas in the photopic condition the response in most of them was accompanied by a resistance increase, at least in their initial part and showed a reversal at -53 -+ 11 mV. The results suggest that the photoresponse activated by rod input is due to an increase in gNa. In the mesopic condition rod-dominant cells showed complex electrical membrane properties as the result of electric interaction between the above two different ionic mechanisms activated by rod and cone inputs.

Calcium influx and calcium current in single synaptic terminals of goldfish retinal bipolar neurons.

“…This negative shift places the activation range of the Ca2+ current within the physiological operating range of on-type bipolar neurons of goldfish retina. In the dark, the resting potential of these cells in situ is -40 to -50 mV (Saito, Kondo & Toyoda, 1979;Kaneko, Famiglietti & Tachibana, 1979), which is near the level at which Ca2+ current began to activate in our voltage-clamp experiments. In response to light, large-terminal on-bipolar neurons depolarize by 10-20 mV (Saito, Kujiraoka & Yonaha, 1983), bringing the potential into the range in which the Ca2+ current increased rapidly with depolarization (e.g.…”

Regulation of ON bipolar cell activity

“…In this retina, as in the retinas of other lower vertebrates, most classes of ON bipolar cells collect input from both rods and cones. Early studies of the light responses of carp and goldfish retina demonstrated that in these mixed input bipolar cells, light responses arising from rods were associated with a positive reversal potential and a conductance increase, while the light responses originating from cones reversed at negative voltages and were associated with a conductance decrease (Saito et al, 1978;Saito et al, 1979). Note that both conductance mechanisms are functionally similar in that they result in membrane depolarization.…”

An analysis of voltage noise in rod bipolar cells of the dogfish retina.

“…Since light decreases the input resistance of the bipolar cell, it was argued that the effect of the transmitter was to close ionic channels (Kaneko, 1971;Toyoda, 1973;Saito, Kondo & Toyoda, 1979;Ashmore & Falk, 1980a). The reversal potential Er for depolarizing bipolar cells of the dogfish retina was about -8 mV (Ashmore & Falk, 1980a).…”