INVOLVEMENT OF CALCIUM AND CALMODULIN IN TOXOPLASMA-GONDII TACHYZOITEINVASION

The tachyzoite of Toxoplasma gondii must successfully invade a host ce ll before it can replicate, Depletion of the Ca2+ in the external medi um (EGTA) reduced tachyzoite invasion, suggesting that the initial tac hyzoite-host cell interaction is Ca2+ dependent, The interaction of ta chyzoites with host cells was also inhibited by Ca2+ channel blockers (verapamil) and calmodulin antagonists (trifluoperazine, calmidazolium ), The calmodulin concentrated at the apical end of the tachyzoite cou ld be involved in cytoskeleton movement and conoid extrusion, Invasion also depends on changes in tachyzoite cytosolic calcium, Depletion of Ca2+ with A23187+EGTA and release of Ca2+ from intratachyzoite pools (nuclear and perinuclear areas) inhibited invasion, In contrast, Ca-io nophore and thapsigargin which increase host cell cytosolic Ca2+, sign ificantly decreased tachyzoite invasion, We therefore suggest that the effect of the drug is significantly different from the localized Ca2 signal that is produced after parasite attachment to its host cell re ceptors and leads to its internalization into the host cell.