A nutrient-permeable channel on the intraerythrocytic malaria parasite

The intraerythrocytic malaria parasite Plasmodium falciparum faces at least three membranous barriers to acquisition of nutrients from serum: the human erythrocyte membrane, the parasitophorous vacuole membrane (PVM) and the parasite plasma membrane. The PVM is a specialized parasite-derived membrane that separates the parasite from erythrocyte cytosol. I used the patch clamp method to identify and characterize the main transport pathway on the PVM. Gigaohm seals, formed on mature freed trophozoites, revealed a 140 pS channel permeable to both cations and anions on the PVM. This channel is present at high density, is open more than 95% of the time at the PVM resting potential, and is capable of transporting amino acids and monosaccharides across the PVM. This nutrient-permeable channel was then reconstituted into artificial lipid bilayers, where it exhibited similar slope conductances, gating, voltage dependence and permeability to soluble nutrients. In bilayers, the channel was found to have non-saturating kinetics and an effective pore diameter of 23 A. These experiments, together with the patch clamp findings, suggest a high capacity molecular sieve that allows the parasite to acquire soluble nutrients from erythrocyte cytosol.