Developmental changes in energy metabolism ofSchistosoma mansoni and physiological role of oxygen in maintaining parasite function.

The time course of the conversion from a cyanide-sensitive to a cyanide-insensitive energy metabolism in immatureSchistosoma mansoni was followed by correlating transitions in CO2 and lactate formation with physiological properties of the parasite. Volume conducted electrical potentials and measurement of CO2 evolution indicate that 3-hr posttransformational schistosomula are highly sensitive to 1 mM cyanide. By 24 hr after transformation, evolution of CO2 under control conditions is reduced by 77% from 3-hr levels, while lactate excretion rises by 84%. At the 24-hr stage, neither cyanide nor rotenone affects the frequency or magnitude of endogenous electrical transients, but cyanide does eliminate 83 % of the already reduced levels of CO2 evolved in 24-hr schistosomula. The adult parasite evolves a low level of CO2 which is reduced by 88% in the presence of 1 mM cyanide. No significant Pasteur effect is detected, however, and endogenous electrical activity as well as mechanical responses of the adult musculature are unaffected by cyanide exposure. Furthermore, adult schistosomes were not adversely affected in terms of the physiological parameters measured by 24-hr incubations in oxygen-free medium. Adults were only marginally affected by 24-hr exposure to several respiratory inhibitors, but responded rapidly to some uncouplers of oxidative phosphorylation, including 2,4-DNP, carbonyl cyanide 3-chlorphenylhydrazone, and closantel. Our results indicate that schistosomula continue to rely on cyanide-sensitive respiratory components for at least 3 hr after transformation; by 24 hr, however, the parasites are metabolically similar to the adult stage, i.e, they depend on lactate fermentation for most of their energy requirements.