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Diffusion coefficients of retinoids
Christopher S Dodson1, Andrey V Peresypkin, Kalpana Rengarajan
1Department of Ophthalmology, Emory University, Atlanta, GA 30322, USA.
Purpose:
Diffusion coefficients of various retinoids have not been measured previously. It is important to know the diffusion coefficients of the retinoids because this property might be rate-limiting in dark adaptation. Also, retinoid diffusion is important to explore given that rhodopsin regeneration is not impaired in IRBP knockout mice.
Methods:
Measurements of lateral diffusion coefficients (D) of 9-cis-retinal, all-trans-retinal, and all-trans-retinol were made by Fourier transform pulsed-gradient spin-echo NMR measurements (FT-PGSE NMR) in several solvents. Also,(3)H-all-trans-retinoic acid was used to measure diffusion from an aqueous agarose matrix and absorption into a toluene based scintillation fluid in a biphase assay.
Results:
In a 1:1 mixture of CD(3)OD:D(2)O the D's of the retinoids were, 2.4 to 3.0 x 10(-6)cm( 2)/s. In the biphase assay,(3)H-all trans-retinoic acid exhibited a diffusion coefficient of 2.3 x 10(-6)cm(2)/s.
Conclusions:
The lower than expected D for retinoids and our calculations suggest that mechanisms in addition to pure aqueous diffusion may be needed to account for normal rhodopsin regeneration rates in the mammalian retina.