Schistosoma mansoni: Calcium efflux and effects of calcium-free media on responses of the adult male musculature to praziquantel and other agents inducing contraction

When male Schistosoma mansoni were incubated in a Ca²⁺-free medium their responsiveness to the contracture inducing agents, praziquantel (PZ), dinitrophenol (DNP), 60 mM K⁺ (high K⁺), ouabain, and low temperature, was rapidly attenuated. After 5 min in a zero Ca²⁺ medium the responsiveness to PZ was reduced by 60% but a residual response of 20% remained even after 40 min in a calcium-free medium. The contracture induced by ouabain or low temperature was totally lost within 1 min exposure to a zero Ca²⁺ medium. The efflux of ⁴⁵Ca²⁺ from parasites incubated in a medium containing no Ca²⁺ closely parallels the drop in responsiveness of their musculature to high K⁺, DNP, and PZ. The total amount of Ca²⁺ in the parasite was reduced by only 30% after 60 min in zero Ca²⁺ medium. A relatively rapid exponential decline in muscle tension was noted when parasites, previously treated with PZ, high K⁺, or DNP, were transferred to a medium containing these agents but with no Ca²⁺. Parasites that had been contracted with ouabain or low temperature showed no significant relaxation 16 min after transfer to a zero Ca²⁺ medium. The ⁴⁵Ca²⁺ efflux from worms bathed in zero Ca²⁺ medium was not significantly altered by the presence of ouabain. These results suggest the presence of active Ca²⁺ transport at the level of the parasites' muscle membranes.