Effect of saturated and unsaturated fatty acids on the oxidative metabolism of human neutrophils. The role of calcium ion in the extracellular medium.

The ability of fatty acids to stimulate the generation of superoxide anion (O2-) by human neutrophils was investigated with respect to their Krafft points. Saturated (myristic acid) and unsaturated (elaidic and oleic acid) induced a marked O2- generation and release from human neutrophils at pH 7.4 in the absence of Ca2+, while 0.3 mM Ca2+ inhibited both myristic acid and elaidic acid-induced O2- release. [14C]Myristic acid association with neutrophils was reduced by addition of Ca2+, whereas oleic acid association was not affected. When the pH of the reaction mixture was lowered to 6.4, 0.6 mM Ca2+ did not inhibit the O2- generation by human neutrophils. These results indicate that the inhibitory effect of Ca2+ on the fatty acid-induced O2- generation might be due to the ionic interaction between the carboxyl group of the fatty acid and Ca2+. Furthermore, 11-methyltridecanoic acid, a branched isomer of myristic acid, which showed the low Krafft point even in the presence of Ca2+, stimulated O2- generation by human neutrophils not only in the absence but also in the presence of 0.6 mM Ca2+. The effect of Ca2+ on the fatty acid-induced O2- generation by neutrophils was discussed with reference to its possible relationship to the Krafft point.