Energy-dependent export of leukotriene B4 in Xenopus oocytes

The export of leukotriene (LT) B4 was studied using the Xenopus oocyte system. The oocytes were microinjected intracellularly with [3H]LTB4, and the export/injection ratios were determined. The ratios decreased with increasing doses of LTB4, converging upon 4%. The export was temperature-dependent and decreased with ATP depletion, thereby suggesting that the export is energy-dependent and carrier-mediated. The LTB4 export was inhibited by 6-trans-LTB4 and its 12-epi isomer, but much less by LTD4. Neither verapamil nor quinidine significantly inhibited LTB4 export. These results suggest that oocytes have an export system specific for LTB4 and its isomers, and that the multidrug-resistant transporter is not involved in this system. By contrast, much of platelet-activating factor, another lipid mediator, was retained in oocytes at different temperatures after injection. It was thus shown that the two potent lipid mediators are exported from cells in a different manner and that oocytes are a good model for analyzing export systems for bioactive mediators.