Effects of riboflavin-sensitized photo-oxidation on choline metabolism in cultured rat lenses.

Previous studies have indicated that photosensitized oxidation of cultured rat lenses greatly decreases their ability to accumulate labeled choline from the medium. This effect required a photosensitizer, light, and oxygen. Choline accumulation appeared to be somewhat more sensitive to damage than 86Rb accumulation. The following studies were designed to test the relative sensitivity of choline metabolism to photo-oxidation and to determine whether the primary site of damage involved the choline carrier or the choline phosphorylation mechanism (which traps choline in the lens). The ATP concentration and the rates of 3H-choline transport, choline phosphorylation, and 86Rb transport were measured in individual rat lenses. These parameters were compared in lenses cultured for 1-16 hr with or without 50 microM riboflavin. In the lenses exposed to riboflavin and light, choline uptake decreased to less than 40% of control within 4 hr, while 86Rb uptake decreased more slowly, approaching 40% of control at 12 hr. The difference in damage between the two transport systems was especially evident at 4-8 hr. Subsequent to the effect on choline transport, photo-oxidation also caused a progressive and concurrent decrease in both ATP concentration and choline phosphorylation. The time course of the observed changes demonstrated that the early decrease in accumulation of 3H-choline in these lenses resulted from effects on transport rather than from decreased conversion to phosphorylcholine.