Ca2+‐Dependence of Conoid Extrusion in Toxoplasma gondii Tachyzoites
- 1 March 1996
- journal article
- Published by Wiley in The Journal of Eukaryotic Microbiology
- Vol. 43 (2), 120-127
- https://doi.org/10.1111/j.1550-7408.1996.tb04491.x
Abstract
The role of Ca2+ in conoid extrusion was investigated in isolated Toxoplasma gondii tachyzoites by treatment with Ca2+-ionophores, Ca2+-chelating agents and an inhibitor of the Ca2+-ATPase at the endoplasmic reticulum. The results were evaluated by light phase-contrast microscopy and electron microscopy. lonomycin (0.5-1 μM) caused an immediate and sustained extrusion of the conoid in up to 80% of the tachyzoites, depending on the concentrations of ionophore and Ca2+ in the medium. However, over 50% of the tachyzoites extruded the conoid when treated with ionomycin in Ca2+-free saline complemented with EGTA. The effect of ionomycin was reversible and could be induced a second time in about half of the responsive population. Similar results were obtained with A23187. Conoid extrusion induced by ionomycin in Ca2+-free medium was almost completely abolished when the tachyzoites were previously loaded with a permeable compound known to chelate intracellular Ca2+ (BAPTA/AM; 25μM). On the other hand, exposure of tachyzoites to the Ca2+-ATPase inhibitor thapsigargin (0.5-1μM) produced significant extrusion of the conoid. Tachyzoites loaded with BAPTA/AM as well as those treated with ionomycin, i.e. with conoids paralyzed in opposite positions, had a diminished capacity to invade cultured epithelial cells. A substantial reduction in the response to stimulation by ionomycin was found also in parasites treated with cytochalasin-D, a drug that depolymerizes actin-filaments. The results suggest that Ca2+-release from internal stores may act as a key signal to activate a mechanism of conoid extrusion probably mediated, at least in part, by actin-filaments.Keywords
This publication has 36 references indexed in Scilit:
- Effect of Extracellular Ions on Motility and Cell Entry in Toxoplasma gondiiThe Journal of Protozoology, 1990
- Effects of cytochalasin and phalloidin on actin.The Journal of cell biology, 1987
- Effects of Extracellular Potassium on Acid Release and Motility Initiation in Toxoplasma gondiiThe Journal of Protozoology, 1987
- Cytoskeleton of Toxoplasma gondii1The Journal of Protozoology, 1987
- Scanning Electron Microscopy of Toxoplasma gondii: Parasite Torsion and Host‐Cell Responses during Invasion1The Journal of Protozoology, 1984
- Immunofluorescent Localization of Myosin at the Anterior Pole of the Coccidian, Toxoplasma gondi1The Journal of Protozoology, 1983
- Are rhoptries of coccidia really extrusomes?Journal of Ultrastructure Research, 1983
- Secretion from the Rhoptries of Toxoplasma gondii during host-cell invasionJournal of Ultrastructure Research, 1983
- Fine Structure of Penetration of Cultured Cells by Isospora canis SporozoitesThe Journal of Protozoology, 1978
- The behaviour of Toxoplasma gondii on serum-agar cultureParasitology, 1954