Vitamin A receptors. Retinoic acid binding in ocular tissues

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Abstract
Analysis of the sucrose-density patterns of the 110,000 g supernatant fractions of adult and fetal retina and pigment epithelium [chicken, bovine, rhesus monkey] showed they contain a limited number of highly specific binding sites (receptors) for [3H]retinoic acid that sedimented at approximately 2S. Binding in pigment epithelium was higher than in any tissue yet reported. A 5S binding component was also observed and was probably due to serum contamination. Fractionation studies indicated that [3H]retinoic acid binding in the retina was lower in the photoreceptor units than in the retinal inner layers. This was in contrast to previous results that showed greater [3H]retinol binding in photoreceptors. Studies with dystrophic human and rat retinas, which lack the photoreceptor layers, confirmed that [3H]retinoic acid binding was greater in the non-photoreceptor layers of the retina. No specific [3H]retinoic acid binding was found in corneal epithelium, although endothelium and the conjunctiva demonstrates specific 2S binding. Such differences in retinol and retinoic acid binding may indicate different roles for the 2 compounds in ocular tissues.