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E Frixione

Publications and source records attributed to E Frixione.

22 records · Page 2Linked to original sources
PubMedDate not supplied

Divalent cation and ATP dependent motility of Toxoplasma gondii tachyzoites after mild treatment with trypsin.

Large percentages of Toxoplasma gondii tachyzoites could be induced to display two types of movement associated with active invasive behavior by exposing them for 1 min to 0.002% trypsin in phosphate-buffered saline (PBS). The motile activity, consisting of clockwise rotation around the posterior end (about 20 revolutions per min) and twirling-gliding over a poly-L-lysine substrate (1.2 +/- 0.2 microns/s standard deviation), was observed and recorded by video-enhanced contrast microscopy. The number of active tachyzoites reached a maximum 1 min after trypsinization; the motile response of the population lasted for about 5 min. Activation was prevented by soybean trypsin-inhibitor, and could not be induced again in previously treated specimens. Electronmicroscopy of trypsinized tachyzoites fixed in the presence of ruthenium-red revealed discrete discontinuities of the plasma membrane, which sealed within 90 min after washing with PBS. Treated tachyzoites were able to invade cultured epithelial cells with a higher relative infectivity than that of untreated parasites. Perfusion of trypsinized tachyzoites with 1 mM of either CaCl2 or MgCl2 and 1 mM ATP increased the number of activated parasites to over 60%; on the other hand, all induced motility was inhibited or blocked by agents that chelate divalent cations. The present preparation, which provided the first serial illustrations of T. gondii movements induced by a defined chemical stimulus, may offer a useful experimental model for the study of motility in this parasite.

Adenosine Triphosphate↗
PubMedDate not supplied

Ca(2+)-dependence of conoid extrusion in Toxoplasma gondii tachyzoites.

The role of Ca2+ 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. Ionomycin (0.5-1 microM) 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 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 Ca2+ (BAPTA/AM; 25 microM). On the other hand, exposure of tachyzoites to the Ca(2+)-ATPase inhibitor thapsigargin (0.5-1 microM) 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.

Actins↗
PubMedDate not supplied

Germination of Nosema algerae (Microspora) spores: conditional inhibition by D2O, ethanol and Hg2+ suggests dependence of water influxupon membrane hydration and specific transmembrane pathways.

The germination of microsporidian spores under conditions expected to affect water flow across the plasma membrane-wall complex was studied by assessing their responses to in vitro stimulation with Na+ or K+. Partial or full substitution of common water with D2O, which more effectively coats ions and electrostatically-charged cell surfaces with relatively stable hydration layers, delayed and inhibited spore germination in a concentration-dependent manner; yet, preincubation in 100% D2O did not change the normal response to standard stimulation. Water structure-breaking conditions, such as an increase in temperature (within the 15 degrees C to 40 degrees C range) or in ionic strength (1- to 10-fold normal), opposed the inhibition by D2O and allowed significant stimulation by Li+, the monovalent cation with the largest hydration diameter and a usually weak stimulant action on the spores. Ethanol, known to reduce water permeation across cell membranes and phospholipid bilayers, also caused a powerful and dose-dependent (1% to 4% v/v) inhibition of spore germination, but pretreatment with ethanol did not affect the normal response. HgCl2, an inhibitor of specific water channels, blocked spore germination at just 250 microM in the normal stimulation solution irrespective of the temperature, and permitted only a delayed response in high salt stimulation solutions. However,the inhibition by Hg2+ was abolished by the simultaneous presence of 2-mercaptoethanol in the medium. These results suggest (1) that spore germination is keenly dependent upon the hydration states of both the plasma membrane-wall complex and the stimulant ions, and (2) that osmotic water flows into the spores through specific transmembrane pathways with critical sulfhydryl groups, i.e., analogous to the water channels that facilitate water movements across the plasma membranes of highly permeable cells.

Animals↗