Figure 4.

Sensitivity (I_1/2) and kinetics of M/L-cone photoresponses in Irbp^−/−Tα^−/− mice. Normalized averaged intensity-response relations of isolated retinas (A) and eyecups (B). Points were fitted with Naka-Rushton hyperbolic functions, as follows:

$$\frac{R}{R_{\text{max}}}=\frac{I^n}{I^n+I_{1/2}^n},$$

where R is the transient-peak amplitude of response, R_max is the maximal response amplitude, I is the flash intensity, n is the Hill coefficient (exponent), and I_1/2 is the half-saturating light intensity. A, Retinas: Irbp^+/+Tα^−/− (n = 13), Irbp^−/−Tα^−/− (n = 11). Half-saturated intensities (I_1/2) were 4.5 × 10⁴ and 2.0 × 10⁴photons µm⁻², and exponents were 0.71 and 0.77, respectively. B, Eyecups: Irbp^+/+Tα^−/− (n = 7), Irbp^−/−Tα^−/− (n = 7). Half-saturating intensities were 5.5 × 10⁴ and 2.9 × 10⁴ photons µm⁻², and exponents were 0.69 and 0.80, respectively. C, D, Population-averaged normalized responses to 1.7 × 10⁴ photons µm⁻² test stimuli. Error bars represent SEM. C, Retinas: Irbp^+/+Tα^−/− (n = 7), Irbp^−/−Tα^−/− (n = 12). D, Eyecups: Irbp^+/+Tα^−/− (n = 18), Irbp^−/−Tα^−/− (n = 16). Dim flash recovery time constants (τ_rec) determined from single-exponential fits (not shown) were ~ 180 ms (Irbp^+/+Tα^−/−) and 300 ms (Irbp^−/−Tα^−/−), respectively.