Praziquantel, potassium and 2,4-dinitrophenol: analysis of their action on the musculature of Schistosoma mansoni.

Praziquantel (PZ) (10(-6) M), an antischistosomal drug, 60 mM K+ and 2,4-dinitrophenol (DNP) induce a rapid contracture of the musculature in adult male S. mansoni. This event is accompanied, except for DNP, by an increased accumulation of 45Ca2+ in the parasite. K+-induced contractures had phasic and tonic components while DNP and PZ produced only tonic contracture of the parasites musculature. The Ca2+ antagonist, D-600 (10(-4) M) as well as La3+ (10 mM) and Co2+ (10 mM) prevented the 45Ca2+ accumulation produced by high K+. La3+ and Co2+ blocked the tension increasing effects of high K+; D-600 blocked only the tonic contractures. D-600 and Co2+ did not prevent the 45Ca2+ increase produced by PZ but La3+ did. D-600 did not block the PZ response but Co2+ and La3+ partially attenuated it. La3+ also partially attenuated the DNP response. Co2+ and D-600 prevented sustained contractures in response to DNP. Thus, although K+, PZ and DNP have the same final effect on the musculature of S. mansoni, it appears that their effects are not mediated by the same mechanisms.