Fig. 5.

Mean stimulus response curves (n = 5) of Rpe65+/+ (squares) and Rpe65−/− mice treated with 2.5 (filled circles), 1.25 (open circles), 0.25 (filled triangles), and 0 (brown circles) mg of 9-cis-retinal. The differences in light sensitivity were evaluated by comparing the half-saturating flash intensity (I₀) obtained from fitting the mean data with an equation for exponential saturation (38).

$$ECA=A\cdot QE\cdot (1-{10}^{\alpha l})$$ (Eq 1)

where R is the peak amplitude of the response, R_max is the amplitude of the maximum response, and i is the flash strength in photons/μm². The solid lines are the exponential saturation function (Equation 3) fitted to data with I₀ (equivalent 500 nm photons/μm²): 25 (Rpe65+/+), 164 (2.5), 1995 (1.25), 3929 (0.25), and 3714 (0 mg of 9-cis-retinal). Inset, the kinetics of responses adapted by similar amounts (∼4-fold) by steady background illumination (336 equivalent 500-nm photons/μm²/s, black traces) in a Rpe65+/+ rod and by dark light (free opsin) in rod from Rpe65−/− mouse treated with 1.25 mg of 9-cis-retinal. Each trace is from a single rod and is the mean of 10–20 flashes either 6.25 (wild type) or 910 (Rpe65−/− 1.25 mg of 9-cis-retinal (500 nm photon/μm²/flash).