Evidence for the occurrence of respiratory electron transport in adult Brugia pahangi and Dipetalonema viteae

Abstract

Mixed-sex adult stages of Brugia pahangi and Dipetalonema viteae, in the absence of exogenous substrate, consumed oxygen at rates of 4.18 +/- 0.38 and 2.12 +/- 0.20 ngatoms O2 min-1 mg-1 dry wt. respectively. When calculated on a unit dry weight basis the endogenous O2 consumption rates (E-QO2) of mature adult male macrofilariae of B. pahangi and D. viteae were significantly greater than those of mature females, although the E-QO2 calculated per individual worm was essentially similar irrespective of sex. When assayed as separate unisexual groups, the oxygen uptake of male and female macrofilariae of both species was inhibited by classical inhibitors of respiratory electron transport (RET), and showed classical substrate bypass phenomena in response to succinate and ascorbate, N,N,N',N'-tetramethyl-p-phenylenediamine with respect to the RET inhibitors rotenone (inhibitor of complex I) and antimycin A (inhibitor of complex III). Since male worms elicited similar responses to the classical RET inhibitors as did mixed-sex and/or adult female populations, the possibility that developmental stages contained within the female filariids were contributing in any significant manner to the overall responses observed with the RET inhibitors can be discounted. Such responses as observed with live-intact macrofilariae are normally elicited only by mitochondrial preparations and suggest that the cuticles of both species are permeable to rotenone, succinate, antimycin A, N,N,N',N'-tetramethyl-p-phenylenediamine, azide and cyanide. The uncoupler 2,4-dinitrophenol stimulated the endogenous rate of oxygen consumption (E-QO2) of intact B. pahangi at 33-160 microM, indicating the probable occurrence of RET-coupled oxidative phosphorylation. Higher concentrations of 2,4-dinitrophenol proved inhibitory. Respiratory studies on subcellular fractions substantiated the responses elicited by the intact parasites, suggesting the presence of antimycin A-sensitive and -insensitive RET pathways capable of utilising alpha-glycerophosphate, succinate, and malate as substrates. Both B. pahangi and D. viteae macrofilariae therefore probably possess branched RET-pathways bifurcating on the substrate side of RET-complex III. The rates of substrate oxidation in terms of QO2 mg-1 mitochondrial protein compare well with those observed with other nematode parasites.