The Entamoeba histolytica EhPgp5 (MDR-like) Protein Induces Swelling of the Trophozoites and Alters Chloride-Dependent Currents in Xenopus laevis Oocytes

Entamoeba histolytica , the protozoan responsible for human amoebiasis, presents the multidrug resistant phenotype due to the expression of the E. histolytica P-glycoproteins EhPgp1 and EhPgp5. Here, we studied the protein EhPgp5 encoded by the EhPgp5 gene in emetine-sensitive trophozoites transfected with the pEhNEOPgp5 plasmid carrying the EhPgp5 gene. The transfected trophozoites increased their drug resistance slightly, but became bigger and globular. To investigate other EhPgp5 functions further, we microinjected the EhPgp5 mRNA in Xenopus laevis oocytes. Microinjected oocytes expressed EhPgp5 protein in their membranes and exhibited an ion current not present in the control oocytes. The antisense EhPgp5AS transcript, co-injected with the EhPgp5 mRNA, abolished the exogenous current, showing its specificity. Exogenous current was outward during depolarizing pulses. Reduction of the extracellular Cl - concentration displayed a reversible decrease of the current amplitude. Niflumic acid, 4,4-diisothiocyanatostilbene-2, 2′-disulfonic acid, and other Cl - channel blockers abolished the exogenous current, which was poorly modified by verapamil and changes in osmolarity of the medium. Our results suggest that the EhPgp5 protein could function as a Cl - current inductor and as a coadjuvant factor to avoid drug accumulation in the cell.