Tachyzoite calcium changes during cell invasion by Toxoplasma gondii

Abstract

The invasion of host cells by the obligate intracellular protozoan parasite Toxoplasma gondii is calcium dependent. We have identified two calcium storage areas in tachyzoites, the endoplasmic reticulum and vesicles that contain high concentrations of calcium as amorphous calcium phosphate precipitates. Our data indicate that these vesicles slowly lose their calcium during the intracellular development of the tachyzoite as their nucleus phosphorus content increases. We found fluctuations in the sulfur content of the tachyzoite during invasion following the exocytosis of protein from the secretory organelles, with a loss of sodium and chlorine, and the uptake of potassium from the host cell cytoplasm. We demonstrated that penetration of the tachyzoite into the host cell was accompanied by increases in the concentrations of phosphorus and sulfur in the host cell nucleus, probably due to increased transcription. The cytosol sodium concentrations decreased, while the potassium content increased. Thus, the subcellular element distribution of tachyzoites and host cells changes during invasion and intracellular growth of the parasites. In addition, our results indicate that tachyzoite calcium might be involved in the egress of the parasite from the host cell.

Toxoplasma gondii : changes of transepithelial ion transport in infected HT29/B6 cell monolayers

“…Cl ) secretion could also have been caused by an increase of [Cl ) ] i in T. gondii-infected host cells as reported by Bouchot et al (1999): while the Cl ) concentration in the tachyzoite cytoplasm decreased, the host cell Cl ) concentration increased at 6 h p i. In contrast, an influence of host cell intracellular Ca 2+ concentration on Cl ) transport does not seem probable.…”

“…Studies on alterations of intracellur ion concentrations after infection with T. gondii have so far only been carried out in human monocytes and showed a decrease of sodium concentration in the cytosol associated with increased potassium and chloride concentrations. The infection results in a hyperpolarization of the host cell plasma membrane within 6-24 h (Bouchot et al 1999).…”

Detection and Localization of a Ca2+-ATPase Activity in Toxoplasma gondii.

“…The sudden high calcium concentration in the conoid may activate rhoptry Ca-ATPases, loading these compartments with calcium and causing their contents to discharge with a similar function to a SERCAlike pump. Once inside the cell, and during its replication, there is a release of calcium from the acidocalcisomes (Bouchot et al,1999), leading to an increase in cytosolic calcium. This cytosolic Ca increase should activate Ca 2+ -transport ATPase in the dense granules, enabling them to discharge their proteins into the PV.…”

“…The immunolabelling of the Ca 2+ -ATPase was distributed in the membrane complex, rhoptries, dense granules, nucleus and vesicles with high calcium concentrations (Bouchot et al, 1999) as illustrated in Fig. 5.…”

“…Lastly, mobilization of intra-tachyzoite calcium appeared to be essential for the completion of invasion (Pezzella et al, 1997). We have identified two calcium storage compartments in tachyzoites, the endoplasmic reticulum and vesicles containing amorphous calcium phosphate precipitates (Bouchot et al, 1999). The cytoplasmic concentration of calcium is regulated and the Ca stores loaded in eukaryotic cells largely by the operation of calcium pumps that transport calcium across the cell membranes.…”