We analyzed visual-cycle retinoids in
CRBPI −/− and wt mice during recovery from a flash to determine whether the absence of CRBPI affects the flow of retinoids. HPLC traces obtained 15 minutes after a flash are shown in
Figure 2 . Retinyl esters were reduced in
CRBPI −/− mice, and all-
trans-retinol was elevated, relative to levels in wt control animals. A more detailed analysis of visual-cycle retinoid intermediates is shown in
Figure 3 . The flash used in these experiments in wt mice bleached approximately 35% of the rhodopsin, which was reflected in a corresponding decrease in the amount of 11-
cis-retinal in the retinoid profile (
Fig. 3 , top). The levels of all-
trans-retinal and all-
trans-retinyl esters increased transiently during recovery from the flash, as the bolus of retinoid released by photoisomerization made its way around the visual cycle. The concentrations of other visual-cycle retinoids were not appreciably altered during the recovery, indicating that reactions leading to their utilization are rapid, relative to the reduction of all-
trans-retinal and to the isomerization of all-
trans- to 11-
cis-retinoid, as noted earlier.
5 The distribution of retinoids in dark-adapted
CRBPI −/− mice was similar to that in the wt control mice, except that retinyl esters were reduced to approximately one third the wt amount (
Fig. 3 , bottom). During recovery from a flash, both all-
trans-retinal and all-
trans-retinyl esters accumulated transiently, as observed in the wt. However, all-
trans-retinol also increased transiently, suggesting that a new slow step had been introduced into the visual cycle.