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

Abstract

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 x 10(-6) M. Digoxin and digoxigenin act in a similar manner with a relative potency of ouabain approximately or equal to digoxin greater than 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 temperature below 30 degrees 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 x 10(-5) M). Decreasing temperature of the bathing medium also causes an accumulation of Na+ as well as a K+ 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.