Fig. 4.

A, Response families of cone-driven b-waves for 361 and 513 nm flashes for a GRK1 −/− mouse; each trace is the average of three to five individual responses. The 361 nm flash intensities were (from lowest to highest intensity) 740, 1400, 4300, 7200, and 13,500 photons μm⁻² at the cornea (estimated to produce from 104 to 1900 photoisomerizations in the UV cones), and the 513 nm intensities were 2100, 4200, 8800, 21,500, and 90,000 photons μm⁻² at the cornea (estimated to produce 360 to 15,000 photoisomerizations in the M cones). Thetopmost trace in the 361 nm column is the response to a “white” saturating flash isomerizing ∼1.2% of the “green” and 0.09% of the UV cone pigment. B, Amplitude versus intensity data for GRK1 −/− mice (filled symbols, n = 4) and Arrestin −/− mice (open symbols, n = 4) obtained with flashes of 361 nm (symbols including dots) and 513 nm (not dotted), under cone-isolation conditions, as in A. Eachsymbol represents the normalized peak amplitude of a cone-driven b-wave response (points derived from the responses illustrated in A are shown as filled orfilled + dotted circles); peak amplitudes were measured after filtering responses at 11 Hz to remove oscillations (see Materials and Methods). The peak amplitudes were normalized by dividing them by the saturating amplitude, obtained in response to the white flash (W on abscissa). The flash intensities for each animal's data were scaled by a single, common factor; this factor was the intensity at 513 nm (I₅₁₃) estimated by linear interpolation to produce a response of 20% saturated amplitude (dashed line). Two saturation functions (unbroken lines), having the form r_peak/r_max = 1 − exp (−S̄_λĪ_λ) have been plotted through the data, where I_λ is the scaled flash intensity and S̄_λ is a wavelength-dependent sensitivity factor; the black curve was arranged to intercept the dashed line at the abscissa value 1.0; thegray curve is shifted left by the average relative sensitivity of cone-driven responses of WT mice to these two wavelengths, i.e., by the factorS̄_UV/S̄_M= 5.2 (Table 1). C, Spectral sensitivity of cone-isolated b-wave responses of GRK1 −/− (filled circles) and Arrestin −/− (open circles) compared with WT. For each GRK1 −/− and Arrestin −/− animal, the lateral shift (in logarithmic units) between the two saturation functions best fitting the 513 and 361 nm data in B was measured; the points plotted at ∼361 nm are the mean ± SD of these shifts (the open symbols have been shifted laterally for clarity). The theoretical spectra give the spectral sensitivities of the UV and M cone-driven b-wave responses of WT mice and are replotted without alteration from Figure 6 of Lyubarsky et al. (1999).