Fig. 3.

Color opponency involving shift of photoequilibrium between the dark state and photoproduct of parapinopsin. (A–C) Schematic models of photoequilibrium between the dark state and photoproduct of parapinopsin and changes in the amount of its photoproduct upon different light stimuli under two-photon imaging. Circles filled with purple and green indicate molecules of the dark state and photoproduct of parapinopsin, respectively. Photoequilibrium of parapinopsin under two-photon excitation with 930-nm light (i.e., blue light) is shown with black arrows (A). The shifts in photoequilibrium caused by stimuli of 405- and 588-nm light are shown as purple (B) and orange (C) arrows, respectively. Red arrows indicate the amount of cone transducin (Gt2) activated by the photoproducts, which is equivalent to the hyperpolarization level. Note that the circles and the arrows schematically illustrated in A–D are not quantitatively drawn. The recovery of photoequilibrium to the original state after stimuli turn off under “blue light” condition could account for the antagonistic calcium response under two-photon imaging conditions. (D–F) Calcium level changes upon 405- and 588-nm light stimuli in WT PP cells under two-photon excitation with 930-nm (D; n = 26), 860-nm (E; n = 13), and 1,000-nm (F; n = 13) lights (i.e., blue, violet, and green lights, respectively). Schematic models for shifts in photoequilibrium by light stimuli are also shown in D. Error bars indicate SE. The light intensities of 405- and 588-nm light stimuli in D–F were ∼3.2 × 10¹⁴ and ∼5.4 × 10¹⁷ photons per cm²·s, respectively. The durations of both stimuli were ∼450 ms. ∆F/F values are change rates of normalized fluorescence intensity with the averaged intensity of 10 points before initial light stimuli.