Characterization of a leukotriene C4 export mechanism in human platelets: possible involvement of multidrug resistance-associated protein 1

Abstract

Platelets express leukotriene (LT) C4 synthase and can thus participate in the formation of bioactive LTC4. To further elucidate the relevance of this capability, we have now determined the capacity of human platelets to export LTC4. Endogenously formed LTC4 was efficiently released from human platelets after incubation with LTA4 at 37°C, whereas only 15% of produced LTC4 was exported when the cells were incubated at 0°C. The activation energy of the process was calculated to 49.9 ± 7.7 kJ/mol, indicating carrier-mediated LTC4 export. This was also supported by the finding that the transport was saturable, reaching a maximal export rate of 470 ± 147 pmol LTC4/min × 109 platelets. Furthermore, markedly suppressed LTC4 transport was induced by a combination of the metabolic inhibitors antimycin A and 2-deoxyglucose, suggesting energy-dependent export. The presence in platelets of multidrug resistance-associated protein 1 (MRP1), a protein described to be an energy-dependent LTC4 transporter in various cell types, was demonstrated at the mRNA and protein level. Additional support for a role of MRP1 in platelet LTC4 export was obtained by the findings that the process was inhibited by probenecid and the 5-lipoxygenase-activating protein (FLAP) inhibitor, MK-886. The present findings further support the physiological relevance of platelet LTC4 production. —Sjölinder, M., S. Tornhamre, H-E. Claesson, J. Hydman, and J. Å. Lindgren. Characterization of a leukotrine C4 export mechanism in human platelets: possible involvement of multidrug resistance-associated protein. J. Lipid Res. 1999. 40: 439–446.

Keywords

• active transport
• LTA4 metabolism
• immunoblot
• RT-PCR