Toxoplasma gondii: membrane properties of active energy-dependent invasion of host cells.

The energy-dependence and the significance of membrane stability for the active invasion of host cells by Toxoplasma gondii has been examined in vitro. The penetration of Toxoplasma as measured by the infection rate can be significantly decreased by blocking the parasitic respiratory chain with CN-. The infection rate of blocked parasites is nearly normalized when glucose is present during the infection period. This suggests a strong energy-dependence for the active infection mechanism. DMSO (dimethylsulfoxide) known to increase membrane stability is able to lower the infection rate if either the target or the effector cell is pretreated. Ca2+ was shown to exhibit a similar effect. Procain, which destabilizes the cell membrane, stimulates the invasion of host cells by Toxoplasma parasites. The possible modes of action on the invasion schedule for the different effectors are discussed.