title: Kinetic correlation of the acquisition of resistance to immune attack in schistosomula of Schistosoma mansoni with a developmental change in membrane potential.
abstract: When Schistosoma mansoni cercariae penetrate the skin of the mammalian host they rapidly pass from fresh water to a high salt physiologic environment and transform into schistosomula. Following this transition, the parasites migrate from the skin to the lungs during which time they change from being highly susceptible to immune attack to being refractory, as measured by in vitro cytotoxicity assays. In this study, in vivo or in vitro schistosomula of different ages were examined for developmentally linked changes in membrane function which might correlate with the attainment of the resistant state. In particular, alterations in the distribution of tetraphenylphosphonium (TPP+), a synthetic lipophilic cation which shows a potential dependent partition across membranes, were followed. Three-hour-old schistosomula, which are greater than 75% susceptible to antibody-dependent complement-mediated attack or lymphokine-activated macrophage-mediated cytotoxicity, acquired TPP+ at a similar rate and steady state level to 5-day-old lung worms, which were completely resistant to both these effector mechanisms. The addition of ouabain, a Na+/K+-ATPase inhibitor, caused a 50% decrease in both the rate and steady state of TPP+ uptake by 3 h parasites but had little effect on these parameters in lung worms. Valinomycin, a K+-ionophore, completely inhibited TPP+ influx in both stages. The characteristics of TPP+ efflux from 3-h and 5-day-old parasites preloaded with the cation were found to be dissimilar. Whereas 30% of acquired TPP+ was lost from lung worms within 2 h, only 10% of acquired cation was released from 3-h schistosomula during the same period.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D003602:Cytotoxicity, Immunologic; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D009861:Onium Compounds / Q000378:metabolism; D009943:Organophosphorus Compounds / Q000378:metabolism; D010042:Ouabain / Q000494:pharmacology; D012550:Schistosoma mansoni / Q000254:growth & development / Q000276:immunology / Q000502:physiology*; D014634:Valinomycin / Q000494:pharmacology
chemical_list: D009861:Onium Compounds; D009943:Organophosphorus Compounds; D014634:Valinomycin; D010042:Ouabain; C013289:tetraphenylphosphonium