To investigate how mitochondrial function was affected in
leukotoxin (Lx)-,9,10-epoxy-12-octadecenoate-induced
lung injury, lung mitochondria were extracted from isolated perfused rat lung with or without Lx-induced edematous injury. In the lung treated with 30 mumol of Lx, the mitochondrial respiration rate in states 3 and 4 significantly decreased (without mitochondrial uncoupling) concomitantly with increased release of
lactate dehydrogenase (
LDH), a parameter for cellular damage, into the perfusate and decreased
ATP content in the lung tissue compared with those of untreated lung. Moreover, 30 mumol of Lx resulted in significant inhibition of
cytochrome-c oxidase activity (vs. vehicle control). In contrast, lower doses of Lx (10 mumol) caused lung
edema and cellular damage without evidence for
mitochondrial dysfunction. We also examined cellular and mitochondrial damage in hydrostatic lung
edema. Such
edema showed neither suppressed mitochondrial respiration nor elevated LDH activity in perfusate, although
lung wet weight increased as much as it did after 30 mumol Lx treatment. Our results suggest that the ex vivo
mitochondrial dysfunction is one of the secondary (vs. initial augmented permeability) but specific manifestations of toxicity of Lx, and together with the previous reports, the ex vivo damaging effect of Lx against mitochondria may be ascribed not to its direct action on mitochondria but to Lx-derived cellular mechanism(s).