Sodium-dependent uptake of inorganic phosphate by the intracellular malaria parasite

The unusual channels It's been known for some time that the malaria parasite induces or activates novel channels in the membrane of its host red blood cell, and that because of this, Na + moves into the red cell cytosol, making it a high-Na + environment. New work shows that the parasite takes advantage of this raised Na + to energize the uptake of an essential nutrient, inorganic phosphate. Now the Na + -coupled transporter protein involved has been identified. Malaria parasites trigger an increase in intracellular sodium concentration when infecting red blood cells. This effect provides a direct benefit to the parasite, as it uses the resulting gradient to energize the uptake of phosphate. As the malaria parasite, Plasmodium falciparum , grows within its host erythrocyte it induces an increase in the permeability of the erythrocyte membrane to a range of low-molecular-mass solutes, including Na + and K + (ref. 1 ). This results in a progressive increase in the concentration of Na + in the erythrocyte cytosol 2 , 3 . The parasite cytosol has a relatively low Na + concentration 2 , 4 and there is therefore a large inward Na + gradient across the parasite plasma membrane. Here we show that the parasite exploits the Na + electrochemical gradient to energize the uptake of inorganic phosphate (P i ), an essential nutrient. P i was taken up into the intracellular parasite by a Na + -dependent transporter, with a stoichiometry of 2Na + :1P i and with an apparent preference for the monovalent over the divalent form of P i . A P i transporter (PfPiT) belonging to the PiT family was cloned from the parasite and localized to the parasite surface. Expression of PfPiT in Xenopus oocytes resulted in Na + -dependent P i uptake with characteristics similar to those observed for P i uptake in the parasite. This study provides new insight into the significance of the malaria-parasite-induced alteration of the ionic composition of its host cell.