Ion fluxes changes during early stages of Schistosoma manson

The relationship between the average membrane potential (ΔΨ av ) and sensitivity to complement action of the Schistosoma mansoni parasite was explored. The average membrane potential was estimated by measuring the uptake of [ 3 H]tetraphenyl phosphonium ([ 3 H]Ph 4 P + ). The parasites take up Ph 4 P + indicating the existence of a negative internal plasma potential which is in part dependent on the transmembrane K + gradient, maintained by an active Na + /K + ‐ ATPase. Values for Ph 4 P + uptake could be corrected for mitochondrial accumulation by employing the protonophore carbonylcyanide m ‐chlorophenylhadrazone (CCCP), which collapses the mito‐chondrial potential. The plasma membrane potential derived by this technique was in the range of ‐60 mV. Transformation of this parasite, from its early cercaria stage to the adult worm, was associated with changes in the average membrane potential. The apparent hyperpolarization, which accompanies transformation, may be related to changes in ionic permeability and morphology which occur concomitantly. Complement acting through both the classical and alternative pathways was found to affect the potential of the parasite in its early developmental stages. The correlation between effects on ΔΨ av and sensitivity to complement action, indicates that the complement‐induced changes in ΔΨ av are indeed tightly associated with its mode of action. Treatment of the parasite with complement resulted in net hyperpolarization of the membrane indicating that hyperpolarization rather than depolarization of the membrane is linked to the primary non‐lethal action of complement.