DARK-SUPPRESSION AND LIGHT-SENSITIZATION OF HORIZONTAL CELL RESPONSESIN THE HYBRID BASS RETINA

The responsiveness of luminosity-type horizontal cells, recorded intra cellularly from isolated hybrid bass retinas, decreased after superfus ion for 2 h in constant darkness. Responsiveness was subsequently incr eased (light-sensitized) up to 10-fold after exposure to several short (similar to 0.5 min) periods of continuous illumination. The increase in horizontal cell responsiveness following light-sensitization was d ue to an increase of peak response amplitude rather than a reduction o f peak response time. The increased responsiveness after light-sensiti zation was intensity-dependent with brighter sensitizing stimuli causi ng a greater increase than dimmer stimuli. The extent of LHC dark-supp ression was affected by the time of day, being greater when induced du ring the night than during the day. However, there was no significant difference in horizontal cell responsiveness after light-sensitization in retinas studied during the night compared to those studied during the day The responsiveness of light-sensitized horizontal cells from i solated hybrid bass retinas was found to be suppressed by relatively b rief periods of darkness. The responsiveness of horizontal cells, that were first light-sensitized, decreased by more than 50% following onl y 5 min of darkness. Suppression of light-sensitized horizontal cell r esponsiveness after such a short time in the dark has not been describ ed in other teleost retinas. The suppression of light-sensitized horiz ontal cell responsiveness in hybrid bass retinas may be rapid in compa rison to other teleosts.