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 behavio r by exposing them for 1 min to 0.002% trypsin in phosphate-buffered s aline (PBS). The motile activity, consisting of clockwise rotation aro und the posterior end (about 20 revolutions per min) and twirling-glid ing over a poly-L-lysine substrate (1.2 +/- 0.2 mu m/s standard deviat ion), was observed and recorded by video-enhanced contrast microscopy. The number of active tachyzoites reached a maximum 1 min after trypsi nization; 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 reve aled discrete discontinuities of the plasma membrane, which sealed wit hin 90 min after washing with PBS. Treated tachyzoites were able to in vade cultured epithelial cells with a higher relative infectivity than that of untreated parasites. Perfusion of trypsinized tachyzoites wit h 1 mM of either CaCl2 or MgCl2 and 1 mM ATP increased the number of a ctivated parasites to over 60%; on the other hand, all induced motilit y was inhibited or blocked by agents that chelate divalent cations. Th e present preparation, which provided the first serial illustrations o f T. gondii movements induced by a defined chemical stimulus, may offe r a useful experimental model for the study of motility in this parasi te.