Figure 7.

Single-cell photoresponses of PhLP1-deficient rods. A, B, Representative families of flash responses from 1-month-old PhLP1^+/+Cre⁺ (A) and PhLP1^F/FCre⁺ (B) mice are shown. Test flashes of 500 nm light with intensities of 0.7, 2.2, 6.0, 19.0, 49.5, 157, 557, and 1764 photons μm⁻² (for control rods) or 6.0, 19.0, 49.5, 157, 557, 1764, 5811, and 18415 photons μm⁻² (for PhLP1^F/FCre⁺ rods) were delivered at time 0. The red traces show responses to an identical light intensity (49.5 photons μm⁻²). C, Intensity–response functions for rods from PhLP1^+/+Cre⁺ (n = 22) and PhLP1^F/FCre⁺ (n = 23) mice. Symbols represent the average ± SEM. Data were fit with a hyperbolic Naka–Rushton function and fit parameters are shown in Table 2. D, Amplification of the phototransduction cascade in mouse rods. Population-averaged dim flash responses to light intensities of 49.5 photons μm⁻² for PhLP1^F/FCre⁺ rods and 6.0 photons μm⁻² for wild-type rods were normalized to their corresponding maximum dark currents, r_max. Then the PhLP1^F/FCre⁺ fractional response was scaled down by the factor of 2.2 to make its initial rising phase coincide with that of wild-type response. The light intensity corresponding to this scaled PhLP1^F/FCre⁺ response was thus determined as 49.5/2.2 = 22.5 photons μm⁻². The inset shows the rising phase of the responses on an extended time scale. E, Kinetics of the dim flash responses. Normalized population-averaged dim flash responses to light intensities of 6.0 photons μm⁻² for PhLP1^+/+Cre⁺ (n = 22) and 49.5 photons μm⁻² for PhLP1^F/FCre⁺ (n = 23), demonstrating the decelerated photoresponse inactivation in PhLP1-deficient rods. F, Determination of the dominant time constant of recovery (τ_D) from a series of supersaturating flashes. Linear fits throughout the data yielded τ_D values indicated in Table 2. Values are means ± SEM.