Protein-facilitated export of arachidonic acid from pig neutrophils

Activated neutrophils release a variety of eicosanoids into the extracellular medium including arachidonic acid, 5-hydroxyicosatetraenoic acid, and leukotriene A4 and B4. In this study, the mechanism of arachidonic acid export has been examined using inside-out plasma membrane vesicles from pig polymorphonuclear leukocytes. Tritiated arachidonic acid associated rapidly with the membrane vesicles and crossed the membrane into the intravesicular space in a time-dependent and saturable manner. Half the maximal influx rate was measured at an arachidonate concentration of 5.7 microM, and a maximal influx velocity of 3.0 nmol/mg x min was determined at pH 6.8. Influx into vesicles was sensitive to a number of common anion transport inhibitors including pentachlorophenol, phloretin, diiodosalicylic acid, and quercetin as well as to the proteases trypsin and Pronase, suggesting a protein-dependent process. Furthermore, influx was temperature-sensitive with an energy of activation of 11.6 kcal/mol. Varying extravesicular concentration of ATP, Na+, or K+ had no impact on arachidonate influx, whereas changes in pH had a profound effect; optimum transport activity was observed at an extravesicular pH of 6, whereas raising the pH to 9.5 essentially abolished uptake. These results indicate and initially characterize a novel protein-facilitated arachidonate export mechanism in pig neutrophils.