Rod photoresponse parameters in WT and GCAP1−/− mice.

Parameters for both WT and GCAP1−/− mice average all rods of each type and include “fast” and “slow” rods (see Figures 5 and 6 and the Discussion section). Results are given as mean ± SEM (number of cells recorded, P-value from a Student’s t-test for values less than 0.05). The i0.5 is the flash strength at 500 nm eliciting a half-maximal response, and it varies inversely with sensitivity. SPR amplitude was estimated by dividing the ensemble variance by the mean dim flash response amplitude. Kinetics of the single-photon response were determined from dim flash responses whose amplitude was less than 20% of the maximum. Time to peak was measured from mid-flash to the response peak. Integration time was calculated as the integral of the response divided by response amplitude. Recovery time constant, τr, refers to a fit of the final falling phase of the dim flash response with a single exponential. Saturation time constant, τc, is the slope of the relation between saturation time and the natural logarithm of the flash strength, by linear regression. Rmax is the maximum circulating current recorded from a rod, and fractional amplitude is taken as a ratio of the single-photon-response amplitude to the maximum circulating current from that rod.