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Ca 2+ ‐Dependence of Conoid Extrusion in Toxoplasma gondii Tachyzoites
Author(s) -
MONDRAGON RICARDO,
FRIXIONE EUGENIO
Publication year - 1996
Publication title -
journal of eukaryotic microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.067
H-Index - 77
eISSN - 1550-7408
pISSN - 1066-5234
DOI - 10.1111/j.1550-7408.1996.tb04491.x
Subject(s) - ionomycin , conoid , thapsigargin , bapta , biology , egta , cyclopiazonic acid , biophysics , intracellular , calcium , microbiology and biotechnology , medicine , anatomy
The role of Ca 2+ in conoid extrusion was investigated in isolated Toxoplasma gondii tachyzoites by treatment with Ca 2+ ‐ionophores, Ca 2+ ‐chelating agents and an inhibitor of the Ca 2+ ‐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 Ca 2+ in the medium. However, over 50% of the tachyzoites extruded the conoid when treated with ionomycin in Ca 2+ ‐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 Ca 2+ ‐free medium was almost completely abolished when the tachyzoites were previously loaded with a permeable compound known to chelate intracellular Ca 2+ (BAPTA/AM; 25μM). On the other hand, exposure of tachyzoites to the Ca 2+ ‐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 Ca 2+ ‐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.