Here we show that in vitro supplementation of L1210 murine lymphoblastic leukaemia cells with n-3 polyunsaturated fatty acids results in considerable changes in the fatty acid composition of membrane phospholipids. Incubations for 48 h with 30 μM eicosapentaenoic acid (20:5, n-3; EPA) or docosahexaenoic acid (22:6, n-3; DHA) results primarily in substitution of long-chain n-6 fatty acids with long-chain n-3 fatty acids. This results in a decrease in the n-6/n-3 ratio from 6.9 in unsupplemented cultures to 1.2 or 1.6 for EPA and DHA supplemented cultures, respectively. Coincident with these changes in membrane fatty acid composition, we observed a 5-fold increase in the rate of adenosine (5 μM) uptake via the nitrobenzylthioinosine (NBMPR)-sensitive nucleoside transporter in EPA- and DHA- supplemented L1210 cells, relative to unsupplemented cells. This seemed to result from a decrease in the Km for adenosine from 12.5 μM in unsupplemented cultures to 5.1 μM in DHA-treated cultures. Guanosine (50 μM) transport was similarly affected by DHA with a 3.5-fold increase in the initial rate of uptake. In contrast, pyrimidine transport, as measured by uptake of thymidine and cytidine, was not similarly affected, suggesting that substrate recognition had been altered by fatty acid supplementation. Studies using [3H]NBMPR showed that there was no effect of EPA or DHA on either the number of NBMPR-binding sites or the affinity of these sites for NBMPR. This observation suggests that the increases in adenosine and guanosine transport were not due to increases in the number of transporter sites but rather that EPA and DHA directly or indirectly modulate transporter function.

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