Figure 6.

The lifetime of rhodopsin determines the variability and area of the single-photon responses. A, Multistep shutoff model of the activity of rhodopsin. B, The ratio of the time-to-peak of the time-dependent variance (t _peak,σ²) to the time-to-peak of the mean (t _peak,μ) of the single-photon responses depends on the lifetime of rhodopsin (τ_Rh*). The solid black line is fit to the predicted changes (open circles) in t _peak,σ²/t _peak,μ as a function of τ_Rh*. τ_T* was kept constant at 200 ms. The experimental points (filled circles) are located on the fit at a y-axis location according to the measured t _peak,σ²/t _peak,μ ratio; the resulting x-axis position estimates τ_Rh*. C, τ_Rh* controls the area of the single-photon response. Filled circles are the experimentally determined normalized response areas. These values were positioned on the x-axis using the predicted τ_Rh* determined in B. The solid black line is fit to the predicted changes in response area as a function of τ_Rh*. Insets show the average single-photon response of 1000 simulated trials using the τ_Rh* predicted from the model for each recorded mouse strain. The model captures the relative differences in amplitude and duration of the isolated single-photon responses in wild-type and mutant rods. Error bars are SEM.