PRAZIQUANTEL HAS NO DIRECT EFFECT ON (NA-ATPASES AND (CA2+-MG(2+)ATPASES OF SCHISTOSOMA-MANSONI(+K+))

Therapeutic concentrations of praziquantel produce a rapid and intense contraction of the human flatworm Schistosoma mansoni. As an action o n ATPases responsible for calcium homeostasis arises as a possible exp lanation for the molecular mechanism of this effect, we tested here th e effect of praziquantel on different preparations from male adult wor ms that were previously characterized for their content in (Na++K+)-AT Pase and (Ca2+-Mg2+)ATPase activities from different origins. Concentr ations as high as 100 mu M praziquantel did not inhibit (Na+-K+)-ATPas e from tegument and carcass nor (Ca2+-Mg2+)ATPase from heterogeneous ( P-1) and microsomal (P-4) fractions. As 100 mu M praziquantel was also without effect on calcium permeability of microsomal vesicles activel y loaded with Ca-45(2+), the present results discard three hypotheses recently raised for the mechanism of praziquantel-induced contraction of S. mansoni.