Figure 4.

The time course of retinol formation in salamander red cones containing different visual pigments as assessed by microfluorometry. The normalized relative fluorescence intensity is plotted as a function of time after a >95% bleach in red cones from Ambystoma mexicanum under different visual pigment conditions. Data were normalized relative to the peak value and fitted with a single-exponential function. Red cones contained their native A1/A2 mixture (gray; n = 6; τ = 17.5 ± 1.2 s), or were regenerated with either 11-cis retinal (black; n = 5; τ = 20.8 ± 0.9 s) or 9-DM retinal (red; n = 6; τ = 70.9 ± 6.7 s). Error bars show ± SEM. Note that between the first and second measurements in all three cases, there is a rapid initial increase in fluorescence that is present in all fluorescence recordings; this has been reported previously (Tsina et al., 2004; Ala-Laurila et al., 2006) and is of unknown origin. The inset illustrates an experiment in which the rise and fall of retinol fluorescence were measured in a single red cone from Ambystoma tigrinum under all three visual pigment conditions. First, the red cone was measured with its native pigment (gray squares), then containing 9-DM retinal visual pigment (red circles), and finally containing 11-cis retinal visual pigment (black triangles). 100 µM IRBP was present to facilitate the exchange of chromophore. Data are normalized relative to the peak value.