High voltage malaria parasites.

The malaria parasite is a unicellular organism which, in the course of its complex lifecycle invades the red blood cell of its host. As it grows and replicates it requires a supply of nutrients from the external medium. These are taken up into the infected red blood cell, from the blood plasma, and then from the red cell compartment into the parasite itself. In many cell-types the uptake of nutrients across the surface ‘plasma' membrane is assisted by a small voltage which, in animal cells is typically in the range of 50 to 80 millivolts. We have developed methods for measuring the voltage across the parasite's plasma membrane and have shown it to be approximately 100 mV (inside negative), significantly higher than in the cells of the host. The voltage across the parasite plasma membrane originates from the action of a membrane H(+) pump which extrudes (positively charged) H(+) ions, and is modulated as well by the flow of K(+) ions into the parasite, via membrane K(+) channels.

Following on from our analysis of the size and origin of the parasite's ‘membrane potential' we have shown that it plays a key role in the uptake by the parasite of at least one important nutrient. Choline is a small, positively charged molecule, used by the parasite in the synthesis of new membranes. We have shown that choline is taken up by the parasite, across its surface membrane, via a ‘transporter' that is energised by the transmembrane voltage. The electrical properties of the parasite membrane are therefore of fundamental importance in the biology of this important organism, and the mechanisms underlying these properties may be suitable antimalarial drug targets.

Allen, R.J.W. and Kirk, K. (2004) The membrane potential of the intraerythrocytic malaria parasite, Plasmodium falciparum. J. Biol. Chem., 279, 11264-11272.
Lehane, A.M., Saliba, K.J., Allen, R.J.W. and Kirk, K. (2004) Choline uptake into the malaria parasite is energized by the membrane potential. Biochem. Biophys. Res. Comm. 320, 311-317.