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E Tsina, Y Koutalos, C Chen, RK Crouch, B Wiggert, MC Cornwall; Transport of Retinol from Salamander Rod Photoreceptors by IRBP and Serum Albumin Following Bleaching . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3746.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To investigate the mechanisms by which retinol is transported from vertebrate rod photoreceptors by interphotoreceptor retinoid-binding protein (IRBP) and bovine serum albumin (BSA) following visual pigment bleaching. Methods: Rods were isolated from dark-adapted retinae of larval tiger salamanders and maintained in Ringer's solution in a chamber on the stage of a microscope equipped with a high sensitivity digital CCD camera. The spatial distribution of fluorescence due to retinol (excitation: 360 nm; emission: 540 nm) was measured before and after (every 5 min for 120 min) exposure to bright light calculated to have bleached ≷99% of the visual pigment. The rate of decrease of this fluorescence signal was then measured following treatment with various concentrations of bovine IRBP (3-100 µM) or BSA (1.5-150 µM). Results: Following bleaching light, an intrinsic fluorescence, which we have attributed to the presence of retinol, was observed to increase in the outer segment, reaching a plateau within 30-40 min. When the medium contained no IRBP or BSA, retinol fluorescence declined less than 5% per hour. Treatment with 3 µM and 25 µM BSA, concentrations that cover the range measured in the IPM of a number of vertebrate species [Adler and Edwards (2000), Exp. Eye Res. 70:227-234], resulted in a fluorescence decline of 28% and 43% in one hour, respectively. Similar treatment with IRBP concentrations in the physiological range caused an exponential decline of retinol fluorescence. Exposure to 3 µM and 25 µM IRBP resulted in decline of fluorescence with a half-time of about 25 min and 10 min, respectively. Conclusions: Our measurements are consistent with IRBP and serum albumin, which are both present in the interphotoreceptor matrix, being important for the transport of retinol from photoreceptors following bleaching. The results indicate that IRBP is significantly more effective than BSA in effecting transport of retinol from bleached photoreceptors. Supported by NIH grants EY01157, EY04939, EY11351 and Foundation Fighting Blindness.
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