Rod outer segment membranes: good acceptors for retinoids?

The exchange of all-trans retinoids (retinal, retinol, retinylpalmitate) between PC-vesicles, PC-vesicles and liver microsomes or PC-vesicles and rod outer segment membranes is investigated using 11,12(3)H labeled compounds. In the first two systems, retinal and retinol exchange rapidly, retinyl acetate slowly and retinyl palmitate not at all. Rod outer segment membranes however take up relatively small amounts of retinoids (retinylpalmitate less than retinol less than retinal) and rapidly lose 60-90% of their label in the presence of PC-vesicles. E.G. retinoids clearly favour the PC-vesicle membrane. Apparently, rod outer segment membranes have a much lower affinity for retinoids than other artificial or natural membranes investigated so far.