Entamoeba histolytica: Ouabain-insensitive Na+-ATPase activity

Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, 21941-902 Rio de Janeiro, RJ, Brazil.
Experimental Parasitology (Impact Factor: 1.64). 11/2007; 117(2):195-200. DOI: 10.1016/j.exppara.2007.04.010
Source: PubMed


Our aim was to determine the presence of sodium pumps in Entamoeba histolytica. It is shown through the measurement of ouabain-sensitive ATPase activity and immunoblotting that E. histolytica does not express (Na(+)+K(+))ATPase. On the other hand, we observed a Na(+)-ATPase with the following characteristics: (1) stimulated by Na(+) or K(+), but these effects are not addictive; (2) the apparent affinity is similar for Na(+) and K(+) (K(0.5) = 13.3 +/- 3.7 and 15.4 +/- 3.1mM, respectively), as well as the V(max) (24.9 +/- 1.5 or 27.5 +/- 1.6 nmol Pi mg(-1)min(-1), respectively); (3) insensitive up to 2mM ouabain; and (4) inhibited by furosemide with an IC(50) of 0.12 +/- 0.004 mM. Furthermore, this enzyme forms a Na(+)- or K(+)-stimulated, furosemide- and hydroxylamine-sensitive ATP-driven acylphosphate phosphorylated intermediate.

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    • "Initial experiments involving the heterologous expression of PfATP4 in Xenopus laevis oocyte membranes gave results consistent with PfATP4 having a Ca 2þ -dependent ATPase activity (Krishna et al., 2001); however these results were not replicated in a subsequent study (Rottmann et al., 2010) and, in any case, a Ca 2þ transport function has not been demonstrated directly. Ca 2þ -ATPases are closely related to another class of P-type Na þ - ATPases, the type IID ENA-ATPases (exitus natrus, translating to exit of salt; (reviewed in Rodriguez-Navarro and Benito, 2010)), which efflux Na þ from cells of lower eukaryotes including fungi, bryophytes and several protozoan parasites (including Trypanosoma (Caruso-Neves et al., 1999; Iizumi et al., 2006), Leishmania (Stiles et al., 2003; de Almeida-Amaral et al., 2008) and Entamoeba (De Souza et al., 2007)). "
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    ABSTRACT: The intraerythrocytic malaria parasite, Plasmodium falciparum, maintains a low cytosolic Na(+) concentration and the plasma membrane P-type cation translocating ATPase 'PfATP4' has been implicated as playing a key role in this process. PfATP4 has been the subject of significant attention in recent years as mutations in this protein confer resistance to a growing number of new antimalarial compounds, including the spiroindolones, the pyrazoles, the dihydroisoquinolones, and a number of the antimalarial agents in the Medicines for Malaria Venture's 'Malaria Box'. On exposure of parasites to these compounds there is a rapid disruption of cytosolic Na(+). Whether, and if so how, such chemically distinct compounds interact with PfATP4, and how such interactions lead to parasite death, is not yet clear. The fact that multiple different chemical classes have converged upon PfATP4 highlights its significance as a potential target for new generation antimalarial agents. A spiroindolone (KAE609, now known as cipargamin) has progressed through Phase I and IIa clinical trials with favourable results. In this review we consider the physiological role of PfATP4, summarise the current repertoire of antimalarial compounds for which PfATP4 is implicated in their mechanism of action, and provide an outlook on translation from target identification in the laboratory to patient treatment in the field.
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    ABSTRACT: The malaria parasite Plasmodium falciparum establishes in the host erythrocyte plasma membrane new permeability pathways that mediate nutrient uptake into the infected cell. These pathways simultaneously allow Na(+) influx, causing [Na(+)] in the infected erythrocyte cytosol to increase to high levels. The intraerythrocytic parasite itself maintains a low cytosolic [Na(+)] via unknown mechanisms. Here we present evidence that the intraerythrocytic parasite actively extrudes Na(+) against an inward gradient via PfATP4, a parasite plasma membrane protein with sequence similarities to Na(+)-ATPases of lower eukaryotes. Mutations in PfATP4 confer resistance to a potent class of antimalarials, the spiroindolones. Consistent with this, the spiroindolones cause a profound disruption in parasite Na(+) homeostasis, which is attenuated in parasites bearing resistance-conferring mutations in PfATP4. The mutant parasites also show some impairment of Na(+) regulation. Taken together, our results are consistent with PfATP4 being a Na(+) efflux ATPase and a target of the spiroindolones.
    Cell host & microbe 02/2013; 13(2):227-37. DOI:10.1016/j.chom.2012.12.006 · 12.33 Impact Factor
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    • "These receptors are differentially distributed throughout the nephron, from outer to inner renal cortex, leading to a preferential binding of Ang II either to AT1 or AT2 receptors, respectively. Therefore, the predominant effect of Ang II on the Na+-ATPase in outer cortex would be stimulatory [40, 131–133], while in the inner cortex this peptide would have an inhibitory effect [37]. "
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