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

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Abstract
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.

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