VITAMIN A RECEPTORS: MULTIPLE SPECIES IN RETINA AND BRAIN AND POSSIBLE COMPARTMENTALIZATION IN RETINAL PHOTORECEPTORS

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Abstract
Abstract— As assessed by sucrose density gradient ultracentrifugation, bovine retinal cytosol exhibits 2S and 7S vitamin A binding species (‘receptors’). Upon fractionation of the retina, outer segment photoreceptor units are enriched in 7S receptor whereas the outer segment poor layers of the retina have a decreased amount of 7S receptor. The 2S vitamin A receptor is found both in the photoreceptor fraction and in the rod‐poor layers of the retina. The supernatant fraction of fetal retina demonstrates 2S binding but no 7S binding; a small 7S peak observed in adult pigment epithelial supernatant preparations is also not seen in the supernatant fraction of fetal pigment epithelial cells. The binding pattern in the newborn retina is similar to that in adult retina, i.e. extensive 7S as well as 2S binding. Adult bovine brain exhibits a large 7S receptor peak which is missing in fetal brain supernatant and virtually absent in newborn brain. The 7S receptor may thus be compartmentalized in retinal photoreceptors but is not unique to the retina since it is also observed in brain. The ontogenic patterns in the two tissues are different however.