CARRIER-MEDIATED TRANSPORT OF LIPOXIN A(4) IN HUMAN NEUTROPHILS

Lipoxins and other eicosanoids display potent and selective biological effects on leukocytes. In this study, we utilized radiolabeled lipoxin A(4) ([H-3]LXA(4)) to investigate whether carrier-mediated transport of LXA(4) might occur in human neutrophils. At a concentration of 5 nM, uptake of [H-3]LXA(4), above that due to specific binding to receptors, amounted to similar to 0.6 fmol.10(6) cells(-1) min(-1). This influx was sensitive to a number of anionic inhibitors, including 3,5-diiodosalicylic acid (K-0.5 12 mu M), pentachlorophenol (K-0.5 25 mu M), alpha-cyano-beta-(1-phenylindol-3-yl) acrylic acid, and the organomercurial agents mersalyl (K-0.5 110 mu M) and p-hydroxy-mercuribenzoate. Influx, which was Na+ and membrane voltage independent, exhibited a striking dependence on pH (negative log of dissociation 5.9), results compatible with an H+ + LXA(4) anion cotransport system. The LXA(4) carrier did not appear to interact with arachidonic acid, prostaglandin E(2), 15(S)-hydroxy-(5Z,8Z,11Z,13E)-eicosatetraenoic acid, or the leukotrienes B-4, C-4, and D-4. Moreover, transport activity was not observed in human erythrocytes, lymphocytes, or platelets, but it was inducible in HL-60 cells on differentiation by exposure to retinoic acid. These findings represent the identification and initial characterization of a novel carrier-mediated pathway in human neutrophils that facilitates transport of LXA(4) into cells.