Praziquantel has no direct effect on (Na++K+)-ATPases and (Ca2+-Mg2+)ATPases of Schistosoma mansoni

Therapeutic concentrations of praziquantel produce a rapid and intense contraction of the human flatworm Schistosoma mansoni. As an action on ATPases responsible for calcium homeostasis arises as a possible explanation for the molecular mechanism of this effect, we tested here the effect of praziquantel on different preparations from male adult worms that were previously characterized for their content in (Na++K+)-ATPase and (Ca2+-Mg2+)ATPase activities from different origins. Concentrations as high as 100 μM praziquantel did not inhibit (Na++K+)-ATPase from tegument and carcass nor (Ca2+-Mg 2+)ATPase from heterogeneous (P1) and microsomal (P4) fractions. As 100 μM praziquantel was also without effect on calcium permeability of microsomal vesicles actively loaded with 45Ca2+, the present results discard three hypotheses recently raised for the mechanism of praziquantel-induced contraction of S. mansoni.