Accumulation and incorporation of radiolabeled choline into cultured rabbit lenses: Evidence for a choline transport system

The organic cation choline is readily accumulated and incorporated into lenses. The characteristics of this accumulation and incorporation were studied by culturing rabbit lenses in TC-199 medium containing radiolabeled choline. The accumulation of radiolabel as measured by lens water/media ratios appears to be the result of a transport system. Energy for this system is derived in part from glycolysis and the transport system is not affected by 1 mm-ouabain or 2,4-dinitrophenol. Structurally the transport system is quite specific with neither Tris(hydroxymethyl)aminomethane, tetraethylammonium, dimethylamine, ethylamine nor betaine affecting the uptake of choline. Ethanolamine competed with choline for the transport receptor and was accumulated into the lens while acetylcholine blocked the accumulation without apparent uptake. The metabolic fate of lenticular choline was followed using anion exchange chromatography and 2:1 chloroform-methanol extracts. The radiolabeled choline was rapidly phosphorylated and incorporated into the de novo synthesis of phosphatidyl choline. The phosphorylation was inhibited by both 1 mm iodoacetate and 2,4-dinitrophencl and decreased by lowering the incubation temperature. Ethanolamine, however, did not affect the phosphorylation of choline.