10 Electrical Membrane Properties in the Model Leishmania-Macrophage Marcela Camacho Universidad Nacional de Colombia, Sede Bogotá, and Centro Internacional de Física Colombia 1. Introduction Leishmaniasis, a disease caused by parasites of the genus Leishmania, constitutes a worldwide health problem. Since 1993 the disease has spread over wider areas of the world, and the situation has further deteriorated due to the AIDS pandemic. No vaccine is available to control the disease, and current therapies have problems of resistance, therapeutic failure, and cost (González et al., 2009). In Colombia, the recent incidence of most parasitic diseases has tended to stabilize, but in contrast the last decade has seen a doubling of the incidence of cutaneous Leishmaniasis (INS, 2009). Several reasons explain this, among which climate changes, deforestation, migration, and vector changes are in common with other areas of the world, but local circumstances such as illegal cultivars, the internal armed conflict, and recent health reforms are also important. The parasite Leishmania transits between different environments in its life cycle, from the mosquito gut to the salivary glands, and for a short period in the vertebrate skin, before entering a compartment known as the parasitophorous vacuole (PV) inside macrophages and dendritic cells. The transformation between the two major parasite stages, from promastigote to amastigote, is the result of some of the changes that occur between the mosquito gut and the PV, among which temperature and pH have been implicated (Zilberstein & Shapira, 2004). On the other hand, osmolarity and ionic concentration are known to affect the ability of any cell, presumably including Leishmania, to control membrane potential, ion and nutrient transport, osmolarity, volume, and pH, though the precise effects are yet poorly understood. Our major interest is based on the assumption that Leishmania survival in the macrophage is also the result of the integrated function of the three concentric membranes found by the intracellular (amastigote) form of this parasite: the host cell plasma membrane (i.e., the macrophage plasma membrane), the parasitophorous vacuole membrane (PVM), and the Leishmania plasma membrane. 2. Macrophage plasma membrane In the vertebrate host, Leishmania is an obligatory intracellular parasite that infects cells of macrophagic and dendritic lineage. In other intracellular parasite-host cell relationships, in particular Plasmodium, the demands of the replicating parasite are met by incorporating parasite membrane channels and transporters, or by modulating those of the host cell www.intechopen.com