Transport pathways in the malaria-infected erythrocyte. Their characterization and their use as potential targets for chemotherapy.

The intraerythrocytic malarial parasite is involved in an extremely intensive anabolic activity while it resides in its metabolically quiescent host cell. The necessary fast uptake of nutrients and the discharge of waste products are guaranteed by parasite-induced alterations of the constitutive transporters of the host cell and the production of new parallel pathways. The membrane of the host cell thus becomes permeable to phospholipids, purine bases and nucleosides, small non-electrolytes, anions and cations. While the new pathways are quantitatively unimportant for the translocation of a particular solute, classical inhibitors of native transporters can be used to inhibit parasite growth. Several compounds were found to inhibit effectively the new pathways and, consequently, parasite growth. The pathways have also been used to introduce cytotoxic agents. The parasitophorous membrane consists of channels that are highly permeable to small solutes and display no ion selectivity. Transport of some cations and anions across the parasite membrane is rapid and insensitive to classical inhibitors, and in some cases it is mediated by specific antiporters that respond to their respective inhibitors. Macromolecules have been shown to reach the parasitophorous space through a duct contiguous with the host cell membrane, and subsequently to be endocytosed at the parasite membrane. The simultaneous presence of the parasitophorous membrane channels and the duct, however, is incompatible with experimental evidence. No specific inhibitors have been found as yet that would efficiently inhibit transport through the channels or the duct.