Relationship between intracellular free calcium concentrations and the intracellular development of Toxoplasma gondii.

Abstract

We measured intracellular free calcium concentrations ([Ca++]i) in the subcellular compartments of Toxoplasma gondii infected living cells using microspectrofluorometry and Indo-1 staining. [Ca++]i mapping was defined in infected and uninfected cells and in the neoformed parasitophorous vacuole (PV) 24 and 48 hr after parasite inoculation. At 24 hr after infection, a [Ca++]i gradient (PV/cytoplasm) was observed in favor of the PV in 72% of infected cells (p<0.001). Inside of the PV (lumen and parasites), [Ca++]i values appeared to be homogeneously distributed. At 48 hr after infection, the parasites had replicated and formed typical rosettes of more than 16 parasites. At this step, a positive [Ca++]i gradient (PV/cytoplasm) was detected in all analyzed cells (p<0.001). This result suggests that the PV (lumen and parasites) represents an individual subcellular compartment within the host cell that includes an independent [Ca++]i. Moreover, after 48 hr the cytoplasmic [Ca++]i decreased significantly (39 nM) compared with that measured from uninfected cells (53 nM) (p <0.05). Furthermore, the exit of Toxoplasma mediated by the calcium ionophore 4BrA23187 was preceded by a rise of [Ca++]i to 1 mM in the PV. The [Ca++]i rise and the liberation of parasites from their host appear to be correlated. On the basis of these observations, we suggest that the increase of [Ca++]i in the vacuole may act as a signal that triggers the egress of T. gondii.

Influence of calcium ion on host cell invasion and intracellular replication by Toxoplasma gondii

“…The calcium storage and homeostasis system of T. gondii appears to be similar to that of other eukaryotic cells (Philosoph and Zilberstein, 1989;Bode and Netter, 1996). The calcium ion of host cells also influences cellular replication and the egress of T. gondii tachyzoites (Hupe et al, 1991;Pingret et al, 1996;Moudy et al, 2001). Moreover, when T. gondii contacts a host cell, Ca 2+ signals can stimulate the host cell nucleus to synthesize proteins essential for T. gondii replication (Schwartzman and Pfefferkorn, 1982).…”

Toxoplasma gondii Microneme Secretion Involves Intracellular Ca2+ Release from Inositol 1,4,5-Triphosphate (IP3)/Ryanodine-sensitive Stores

“…Identification of alcohols as potent artificial triggers of microneme secretion led to studies demonstrating that ethanol also raises parasite [Ca 2ϩ ] i levels (11). T. gondii possess several intracellular stores of Ca 2ϩ , including the acidocalcisomes (12), mitochondria, and the endoplasmic reticulum (13). Whether all or some of these stores participate in microneme secretion during host cell invasion is unknown.…”

Ionophore-Resistant Mutants of Toxoplasma gondii Reveal Host Cell Permeabilization as an Early Event in Egress

“…As with many cellular events, Ca 2ϩ has been shown to play a significant role in the signaling of Toxoplasma invasion and egress. Alterations in intracellular [Ca 2ϩ ] have been associated with cytoskeletal rearrangements (12), gliding motility (13), invasion (12,16), intracellular growth (11,19), and host cell egress (9,23,27). There are at least three intracellular Ca 2ϩ stores in this parasite: the endoplasmic reticulum, the mitochondrion, and an unusual compartment called the acidocalcisome (14).…”