Response of endocytosis to altered fatty acyl composition of macrophage phospholipids.

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Abstract
Mouse peritoneal macrophages incubated in serumless medium containing a 19:0 or trans-18:1 fatty acid complexed to bovine serum albumin incorporate the exogenous fatty acid supplement into cellular phospholipids. Within 8 h, 25% of the total phospholipid fatty acids are derived from the supplement, with cell viability remaining > 95%. The incorporation of either of these supplements increases the saturated/unsaturated fatty acid ratio in the phospholipids 2-fold over that of cells cultured in serum and effects striking changes in endocytic activities. The levels of both fluid-phase pinocytosis and receptor-mediated phagocytosis are decreased at all temperatures examined between 15.degree.-37.degree.. The increased degree of saturation of cell phospholipids correlates with decreased endocytic rates for both processes and with increased activation energies (Eact) for phagocytosis. The Eact values for phagocytosis, which range from 54-90 kcal/mol, depend on the supplementation conditions used. Although the levels of pinocytosis are depressed, the Eact values for pinocytosis (17-25 kcal/mol) are not strikingly affected by saturated fatty acid enrichment. The degree of lipid fluidity of macrophage membranes apparently influences both phagocytosis and pinocytosis in macrophages.

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