The effect of light history on the aspartate-isolated fast-PIII responses of the albino rat retina.

PURPOSE To assess the effect of light-rearing history on the photon-capturing ability, amplitude, and kinetics of the fast-PIII response of the retina. METHODS Albino rats were raised on 12-hour light-12-hour dark cycles, with illumination at 3 lux or 200 lux, and killed at approximately 12 weeks. Retinal rhodopsin content was measured spectrophometrically. The morphology of the rod outer segments (ROS) and the thickness of the outer nuclear layer were determined histologically. Electroretinograms of isolated retinas to 3-microsecond flashes were recorded. The kinetics of fast PIII responses were assessed with a model of the phototransduction cascade. RESULTS Total rhodopsin of 200 lux animals was reduced to 60% that of 3 lux animals: 2.3 +/- 0.2 versus 1.4 +/- 0.1 nmol/eye (mean +/- SD). Length of ROS of 200 lux animals was reduced to 68% of the length of that of 3 lux animals: 20.1 +/- 1.2 versus 13.7 +/- 0.5 microns. The saturated amplitude of fast PIII of 200 lux animals was reduced to 56% that of the 3 lux group: 134 +/- 27 versus 239 +/- 37 microV (T = 22 degrees C). Fast PIII responses of both groups are well described by the kinetic model before slow PIII intrusion (up to 100 ms). Estimated kinetic parameters of the transduction cascade did not differ reliably between the two groups. CONCLUSIONS Diminished saturated amplitude of fast PIII in 200 lux animals is accounted for by the hypothesis that fast PIII is directly proportional to the rod photocurrent and by the finding that the ROS of 200 lux animals are short compared to those of 3 lux animals. Similarity in estimated kinetic parameters of phototransduction suggests that the rods of the two groups differ little in the biochemistry underlying the activation phase of phototransduction.