Modification of membrane phospholipid fatty acyl composition in a leukemic T cell line: effects on receptor mediated intracellular Ca2+ increase.

The effect of modifying fatty acyl composition of cellular membrane phospholipids on receptor-mediated intracellular free Ca2+ concentration ([Ca2+]i) increase was investigated in a leukemic T cell line (JURKAT). After growing for 72 h in medium supplemented with unsaturated fatty acids (UFAs) and alpha-tocopherol, the fatty acyl composition of membrane phospholipids in JURKAT cells was extensively modified. Each respective fatty acid supplemented in the culture medium was readily incorporated into phosphatidylinositol, phosphatidylserine, phosphatidylethanolamine and phosphatidylcholine in the JURKAT cells. The total n-6 fatty acyl content was markedly reduced in phosphatidylinositol and phosphatidylcholine of cells grown in the presence of n-3 fatty acids (alpha-linolenic acid, eicosapentaenoic acid and docosahexaenoic acid). Conversely, in the presence of n-6 fatty acids (linoleic acid and arachidonic acid), the total n-3 fatty acyl content was reduced in all the phospholipids examined. In n-3 and n-6 polyunsaturated fatty acid (PUFA) modified JURKAT cells, the total n-9 monounsaturated fatty acyl content in the phospholipids were markedly reduced. Changing the fatty acyl composition of membrane phospholipids in the JURKAT cells appears to have no affect on the presentation of the T cell receptor/CD3 complex or the binding of anti-CD3 antibodies (OKT3) to the CD3 complex. However, the peak increase in [Ca2+]i and the prolonged sustained phase elicited by OKT3 activation were suppressed in n-3 and n-6 PUFA but not in n-9 monounsaturated fatty acid modified cells. In Ca2+ free medium, OKT3-induced transient increase in [Ca2+]i representing Ca2+ release from the inositol 1,4,5-trisphosphate-sensitive Ca2+ stores, were similar in control and UFA modified cells. Using Mn2+ entry as an index of plasma membrane Ca2+ permeability, the rate of fura-2 fluorescence quenching as a result of Mn2+ influx stimulated by OKT3 in n-9 monounsaturated fatty acid modified cells was similar to control cells, but the rates in n-3 and n-6 PUFA modified cells were significantly lower. These results suggest that receptor-mediated Ca2+ influx in JURKAT cells is sensitive to changes in the fatty acyl composition of membrane phospholipids and monounsaturated fatty acids appears to be important for the maintenance of a functional Ca2+ influx mechanism.