The Role of Potassium and Host Calcium Signaling inToxoplasma gondiiegress

AbstractToxoplasma gondii, an obligate intracellular parasite, is capable of invading virtually any nucleated cell. Ca2+signaling is universal and bothT. gondiiand its mammalian host cell will utilize Ca2+signaling to stimulate diverse cellular functions. Egress ofT. gondiifrom the host cell is an essential step for the infection cycle ofT. gondiiand a cytosolic Ca2+increase initiates the Ca2+signaling cascade that culminates in stimulation of motility and egress. In this work we demonstrate that intracellularT. gondiiis capable of taking up Ca2+from the host cytoplasm when this concentration is increased during host signaling events. Both intracellular and extracellular Ca2+sources are important to reach a threshold of cytosolic Ca2+needed for a successful egress. Two peaks of Ca2+were observed in single parasites that egressed with the second peak resulting from Ca2+influx. We patched infected host cells to allow a precise delivery of exact concentrations of Ca2+for stimulating motility and egress. Using this approach, we found that low potassium concentration modulates but do not trigger host cell egress. This is the first study using whole-cell patches to study the role of ions such as K+and Ca2+inT. gondiiegress.