Incubation of exogenous fatty acids with lymphocytes. Changes in fatty acid composition and effects on the rotational relaxation time of 1,6-diphenyl-1,3,5-hexatriene.

Lymphocytes were incubated with various long chain fatty acids bound to albumin. Incubation for 20 h with unsaturated fatty acids resulted in uptake into the neutral lipids and phospholipids. The addition of concanavalin A enhanced the uptake. With the unsaturated fatty acids the rotational relaxation time of 1,6-diphenyl-1,3,5-hexatriene (DPH) was decreased, while with saturated fatty acids there was only a very small effect. The effect on the rotational relaxation times with unsaturated fatty acids was found to be due to the formation of lipid droplets in the cytoplasm. When plasma membrane free of lipid droplets was prepared, there was no effect on the rotational relaxation time despite incorporation of either linoleate or palmitate into the membrane phospholipids. Phospholipid liposomes prepared from plasma membranes obtained from cells which had been cultured with and without exogenous linoleate gave identical rotational relaxation times regardless of the history of the cells from which they were obtained. It is concluded that although the fatty acid composition of lymphocyte plasma membrane can be modified by exogenous fatty acids, there is little effect on the degree of order of the membrane phospholipid fatty acyl chains as monitored by the effects on the rotational relaxation time of DPH.