PROTEIN-FACILITATED EXPORT OF ARACHIDONIC-ACID FROM PIG NEUTROPHILS

Activated neutrophils release a variety of eicosanoids into the extrac ellular medium including arachidonic acid, 5-hydroxgicosatetraenoic ac id, and leukotriene A(4) and B-4. In this study, the mechanism of arac hidonic 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 me mbrane 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 mu M, and a maximal influx velocity of 3.0 nmol/m g x min was determined at pH 6.8. Influx into vesicles was sensitive t o a number of common anion transport inhibitors including pentachlorop henol, phloretin, diiodosalicylic acid, and quercetin as well as to th e proteases trypsin and Pronase, suggesting a protein-dependent proces s, Furthermore, influx was temperature-sensitive with an energy of act ivation of 11.6 kcal/mol. Varying extravesicular concentration of ATP, Na+, or K+ had no impact on arachidonate influx, whereas changes in p H had a profound effect; optimum transport activity was observed at an extravesicular pH of 6, whereas raising the pH to 9.5 essentially abo lished uptake, These results indicate and initially characterize a nov el protein-facilitated arachidonate export mechanism in pig neutrophil s.