Lehane Adele M, Hayward Rhys, Saliba Kevin J, Kirk Kiaran
School of Biochemistry and Molecular Biology, The Australian National University, Canberra ACT 0200, Australia.
J Cell Sci. 2008 May 15;121(Pt 10):1624-32. doi: 10.1242/jcs.016758. Epub 2008 Apr 29.
Chloroquine resistance in the malaria parasite Plasmodium falciparum has made malaria increasingly difficult to control. Chloroquine-resistant parasites accumulate less chloroquine than their chloroquine-sensitive counterparts; however, the mechanism underlying this remains unclear. The primary site of accumulation and antimalarial action of chloroquine is the internal acidic digestive vacuole of the parasite, the acidity of which is maintained by inwardly-directed H+ pumps, working against the (outward) leak of H+. In this study we have investigated the leak of H+ from the digestive vacuole of the parasite by monitoring the alkalinisation of the vacuole following inhibition of the H+-pumping V-type ATPase by concanamycin A. The rates of alkalinisation observed in three chloroquine-resistant strains were two- to fourfold higher than those measured in three chloroquine-sensitive strains. On addition of chloroquine there was a dramatic increase in the rate of alkalinisation in the chloroquine-resistant strains, whereas chloroquine caused the rate of alkalinisation to decrease in the chloroquine-sensitive strains. The chloroquine-associated increase in the rate of alkalinisation seen in chloroquine-resistant parasites was inhibited by the chloroquine-resistance reversal agent verapamil. The data are consistent with the hypothesis that in chloroquine-resistant parasites chloroquine effluxes from the digestive vacuole, in association with H+, via a verapamil-sensitive pathway.
恶性疟原虫对氯喹的耐药性使得疟疾越来越难以控制。耐氯喹的疟原虫积累的氯喹比其氯喹敏感的同类疟原虫少；然而，其背后的机制仍不清楚。氯喹积累和抗疟作用的主要部位是疟原虫内部的酸性消化泡，其酸性由向内的H⁺泵维持，以对抗H⁺的（向外）泄漏。在本研究中，我们通过监测在用 concanamycin A抑制H⁺泵浦V型ATP酶后消化泡的碱化情况，研究了疟原虫消化泡中H⁺的泄漏。在三个耐氯喹菌株中观察到的碱化速率比在三个氯喹敏感菌株中测得的速率高两到四倍。加入氯喹后，耐氯喹菌株中的碱化速率急剧增加，而氯喹导致氯喹敏感菌株中的碱化速率降低。耐氯喹疟原虫中观察到的与氯喹相关的碱化速率增加被耐氯喹逆转剂维拉帕米抑制。这些数据与以下假设一致：在耐氯喹的疟原虫中，氯喹通过维拉帕米敏感途径与H⁺一起从消化泡中流出。
