Carrier-mediated transport of lipoxin A4 in human neutrophils

Lipoxins and other eicosanoids display potent and selective biological effects on leukocytes. In this study, we utilized radiolabeled lipoxin A4 ([3H]LXA4) to investigate whether carrier-mediated transport of LXA4 might occur in human neutrophils. At a concentration of 5 nM, uptake of [3H]LXA4, above that due to specific binding to receptors, amounted to approximately 0.6 fmol.10(6) cells-1.min-1. This influx was sensitive to a number of anionic inhibitors, including 3,5-diiodosalicylic acid (K0.5 12 microM), pentachlorophenol (K0.5 25 microM), alpha-cyano-beta-(1-phenylindol-3-yl) acrylic acid, and the organomercurial agents mersalyl (K0.5 110 microM) 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+ + LXA4 anion cotransport system. The LXA4 carrier did not appear to interact with arachidonic acid, prostaglandin E2, 15(S)-hydroxy-(5Z,8Z,11Z,13E)-eicosatetraenoic acid, or the leukotrienes B4, C4, and D4. 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 LXA4 into cells.