Choline uptake in cultured human Y79 retinoblastoma cells: effect of polyunsaturated fatty acid compositional modifications.

Abstract

Choline uptake in Y79 human retinoblastoma cells occurs through two kinetically distinguishable processes. The high-affinity system shows little sodium or energy dependence, and it does not appear to be linked to acetyl CoA; choline O-acetyltransferase. When the cells are grown in a culture medium containing 10% fetal bovine serum, the high-affinity system has a K'm= 2.16 +/- 0.13 microM and V'max = 27.0 +/- 2.9 pmol min-1 mg-1, whereas the low-affinity system has a k'm = 20.4 +/- 1.3 microM and V'max = 402 +/- 49 pmol min-1 mg-1. Under these conditions, the polyunsaturated fatty acid content of the cell membranes is relatively low. When the polyunsaturated fatty acid content of the microsomal membrane fraction was increased by supplementing the culture medium with linolenic or docosahexaenoic acids (n-3 polyunsaturated fatty acids) or arachidonic acid (n-6 polyunsaturated fatty acid), the K'm of the high-affinity choline transport system was reduced by 40--60%. The V'max also was reduced by 20--40%. Supplementation with oleic acid, the most prevalent monounsaturated fatty acid, did not affect either kinetic parameter. The results suggest that one functional effect of the high unsaturated fatty acid content of neural cell membranes is to facilitate the capacity of the high-affinity choline uptake system to transport low concentrations of choline. This effect appears to be specific for polyunsaturated fatty acids but not for a single type, for it is produced by members of both the n-3 and n-6 classes of polyunsaturated fatty acids.