Membrane potential changes after infection of monocytes by Toxoplasma gondii

Membrane potential changes in host cell plasma membrane were analyzed and t he parasitophorous vacuole membrane (PVM) potential was characterized after infection by Toxoplasma gondii. Human monocytes infested by T. gondii were stained with two membrane potential sensitive dyes, DiOC(6)(3) carbocyanin e and DiSBAC(2)(3) bis-oxonol, before fluorescence emission analysis by con focal laser scanning microscopy. After 24 and 48 h of infection, 34 and 39% , respectively, of monocytes showed several parasites (from two to six) per cell. At these infection times, significant decreases in cytoplasmic emiss ions were observed for both DiOC(6)(3) and DiSBAC(2)(3). Thus, hyperpolaris ation of the host plasma membrane would occur consecutively to infection. I nside the parasitophorous vacuole, the fluorescence intensity of DiOC(6)(3) and DiSBAC(2)(3) increased significantly from 6 to 24 h after infection an d the PVM became less polarised. Involvement of different ATPases in the me mbrane potential of infected monocytes was evaluated with ouabain, DCCD, om eprazole and sodium orthovanadate, ATPase inhibitors. All inhibitors induce d a depolarisation of the plasma membrane. In the parasitophorous vacuole c ompartment, DCCD, omeprazole and sodium orthovanadate but not ouabain cause d a significant depolarisation of the PVM, suggesting that H+, H+/K+ and P- type ATPases were at the origin of the PVM potential. This is the first rep ort showing the presence of ion transporters in the T gondii PVM and the ex istence of at least two members of the P-type family of ion pumps: an elect rogenic H+ ATPase and an electroneutral H+/K+ ATPase. (C) 2001 Australian S ociety for Parasitology Inc. Published by Elsevier Science Ltd. All rights reserved.