Na⁺–K⁺ transport, motility and tegumental membrane potential in adult male Schistosoma mansoni

Summary

Ouabain applied to adult male Schistosoma mansoni causes a large, non-reversible tension increase of the parasite's musculature and elimination of spontaneous contractions. The tension increase and the time-course of tension development caused by ouabain are dose dependent with significant effects obtained at 3 × 10⁻⁶m. Digoxin and digoxigenin act in a similar manner with a relative potency of ouabain ≃ digoxin > digoxigenin. Lowered temperature as well as substitution of Li⁺ for Na⁺ increases muscle tension. The membrane potential recorded from the ventral tegument is also affected by treatments which interact with Na⁺–K⁺ transport systems. Ouabain (0·1 mm) causes a rapid depolarization without a significant effect on membrane resistance. The tegument is depolarized by temperatures below 30 °C. The effect of temperature is readily reversible and the temperature sensitivity is eliminated by pretreatment with ouabain. Substitution of Li⁺ for Na⁺ also causes a depolarization of the tegument. Tracer experiments show both an increase in Na⁺ and a decrease in K⁺ in the parasite within 10 min after treatment with ouabain (1 × 10⁻⁵m). Decreasing temperature of the bathing medium also causes an accumulation of Na⁺ as well as a decrease in the animals. The above results indicate a significant role for active Na⁺–K⁺ transport in muscle contraction and in maintenance of the tegumental membrane potential. The data also suggest that the Na⁺–K⁺ transport in S. mansoni may be electrogenic.