Intensity–response relationships and amplification constants. (A) Normalized photocurrent response (r/r_max) plotted against the number of cone pigment molecules bleached (P*) by the flash (P*/flash). Lines are best fits to Eq. 1 with k set to unity. Values of I_1/2 were as follows: WT, 14 ± 2, n = 5; Gnat1^−/− cones, 940 ± 110, n = 25; Cx36^−/− cones, 990 ± 93, n = 30. (B) Eq. 2 was fit to the first one third to one half of the rising phase of each flash response (inset) to derive amplification constants (A; s^-2). Values of A from Cx36^−/− cones were plotted against flash strength. Inset: Fits to several flashes from the cone in Fig 2 C. The colors of fit lines match the filled symbols.