Toxoplasma need a plasma membrane ion exchanger (right) for a speedy exit.

The protozoan parasite Toxoplasma gondii heads out of its host cell when Ca2+ levels peak in its cytoplasm. Now, Arrizabalaga et al. (page 653) find that proper regulation of these Ca2+ levels, and thus of Toxoplasma exit, requires a Na+/H+ exchanger (NHE), suggesting a link between proton and Ca2+ regulation.

The increase in Ca2+ levels, which can be induced artificially with an ionophore, triggers a series of morphological changes that primes Toxoplasma for both exit and a speedy entrance into a neighboring cell. Death can ensue, however, if the ionophore sticks around while there is no target cell for the parasite to enter; presumably the overstimulated Toxoplasma cannot sustain itself in an activated state.

The authors used this death assay to isolate a mutant...

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