Superoxide formation preceding flight muscle histolysis in Solenopsis: fine structural cytochemistry and biochemistry

In Solenopsis spp., muscle histolysis or breakdown is a normal process in females and is initiated in the flight muscles only immediately after a mating flight. Information regarding the presence of the oxyradical scavenging enzyme superoxide dismutase (SOD) and the formation of the radical oxygen intermediate superoxide (SO) during the early stages of flight muscle histolysis in this insect was investigated. In normal fibrillar flight muscles from control animals, SOD was immunolocalized to vesicular and tubular components of the sarcotubular system. Lanthanum tracer studies indicated that some of these SOD-positive structures might be tubulovesicles continuous with the extracellular space. Following the injection of virgin alates with experimental haemolymph obtained from artificially inseminated females, the membrane delimited elements of the sarcotubular system became increasingly swollen and dilated with time (from 60 to 120 minutes postinjection) with a concomitant decrease in SOD activity and an increase in oxyradical formation. Many similar vesicles were lanthanum-positive. SO was not seen in the sarcoplasmic vesicles and tubules of control insects. The biochemical quantification of SO release over a 2-hour period showed a marked increase in oxyradical formation following treatment with the experimental haemolymph in comparison to control insects. Also, the addition of superoxide dismutase depressed SO formation under these conditions. Despite the histochemical and biochemical changes seen in the muscles of experimental insects, by 2 hours post-treatment there was no evidence of muscle necrosis. From these studies on flight muscle histolysis/necrosis in Solenopsis it appears that the formation of oxyradicals might represent an early event in myopathogenesis and subsequent tissue involution. The generation of SO is more than likely to be associated with alterations in the normal structure, biochemistry and permeability of the biomembranes which delimit the sarcotubular system.