Docosahexaenoic acid (DHA) alters the phospholipid molecular species composition of membranous vesicles exfoliated from the surface of a murine leukemia cell line

Previously, we presented evidence that the vesicles routinely exfoliated fr om the surface of T27A tumor cells arise from vesicle-forming regions of th e plasma membrane and possess a set of lateral microdomains distinct from t hose of the plasma membrane as a whole. We also showed that docosahexaenoic acid (DHA, or 22:6n-3), a fatty acyl chain known to alter microdomain stru cture in model membranes, also alters the structure and composition of exfo liated vesicles, implying a DHA-induced change in microdomain structure on the cell surface. In this report we show that enrichment of the cells with DHA reverses some of the characteristic differences in composition between the parent plasma membrane and shed microdomain vesicles, but does not alte r their phospholipid class composition. In untreated cells, DHA-containing species were found to be a much greater proportion of the total phosphatidy lethanolamine (PE) pool than the total phosphatidylcholine (PC) pool in bot h the plasma membrane and the shed vesicles. After DHA treatment, the propo rtion of DHA-containing species in the PE and PC pools of the plasma membra ne were elevated, and unlike in untreated cells, their proportions were equ al in the two pools. In the vesicles shed from DHA-loaded cells, the propor tion of DHA-containing species of PE was the same as in the plasma membrane . However, the proportion of DHA-containing species of PC in the vesicles ( 0.089) was much lower than that found in the plasma membrane (0.194), and w as relatively devoid of species with 16-carbon acyl components. These data suggested that DHA-containing species of PC, particularly those having a 16 -carbon chain in the sn-1 position, were preferentially retained in the pla sma membrane. The data can be interpreted as indicating that DHA induces a restructuring of lateral microdomains on the surface of living cells simila r to that predicted by its behavior in model membranes. (C) 1999 Elsevier S cience B.V. All rights reserved.