Oxygen consumption (QO) was Measured polarographically in mouse diaphragms stimulated electrically in the presence of (+)-tubocurarine. The preparations showed the basal QO. Electrical stimulation ...facilitated the rate of QO. The effect was evoked repetitively with a small decline. KCN (1 mM) abolished both the basal and the facilitated rates of QO. The facilitated rate of QO depended on the frequency of the stimulation (0.1-3.2 Hz). Under continuous stimulation at 0.1 Hz, veratridine (300 nM) increased the rate of QO with an increment of twitch tension. These effects of veratridine were reduced by ouabain (10 μM). Residual but considerable rates of the facilitated QO were still measured in preparations in which twitch contractions were blocked by dantrolene Na (100 μM) or ethylene glycol (1095 mM). Ouabain (10 uM) and tetrodotoxin (1 uM) reduced the residual facilitation of QO. Veratridine alone did not alter tissue content of Na. Ouabain significantly increased the tissue level of Na. This effect of ouabain was further potentiated by coexistence of veratridine. These results suggest that facilitation of Na-permeability across the cell membrane potentiates the rate of QO and that the inhibition of Na-K-ATPase and/or accumulation of Na in the cell reduce the facilitation of QO induced by electrical stimulation.
1. The effects on oxygen consumption of agents that modify Na(+)-permeability were examined in mouse diaphragm muscle perfused with a bathing solution that contained (+)-tubocurarine in a ...flow-through mode. Twitch tension and levels of Na+ and K+ in the muscle were also measured. 2. Unstimulated preparations decreased the concentration of oxygen in the bathing solution, indicating a basal level of oxygen consumption. Electrical stimulation of the muscle further decreased the concentration of oxygen. Potassium cyanide eliminated both the basal and the stimulated consumption of oxygen. 3. Veratridine facilitated the effect of stimulation at 0.1 Hz on both the consumption of oxygen and the twitch tension. Ouabain antagonized those effects. 4. Twitch contractions were blocked in the presence of dantrolene sodium or by pretreatment with ethylene glycol. Electrical stimulation of such preparations still caused a residual but considerably decreased consumption of oxygen. Ouabain and tetrodotoxin reduced the residual consumption of oxygen. 5. Ouabain significantly increased the levels of Na+ in the tissue, while veratridine alone did not. The effect of ouabain was further potentiated by the simultaneous presence of veratridine. 6. These results indicate that the enhancement of the sarcolemmal permeability to Na+ increases the rate oxygen consumption. This concept supports the hypothesis that Na+ homeostasis depends on energy consumption.
Reactive oxygen species (ROS) production from mitochondrial complex II (succinate-quinone reductase, SQR) has become a focus of research recently since it is implicated in carcinogenesis. To date, ...the FAD site is proposed as the ROS producing site in complex II, based on studies done on Escherichia coli, whereas the quinone binding site is proposed as the site of ROS production based on studies in Saccharomyces cerevisiae. Using the submitochondrial particles from the adult worms and L(3) larvae of the parasitic nematode Ascaris suum, we found that ROS are produced from more than one site in the mitochondrial complex II. Moreover, the succinate-dependent ROS production from the complex II of the A. suum adult worm was significantly higher than that from the complex II of the L(3) larvae. Considering the conservation of amino acids crucial for the SQR activity and the high levels of ROS production from the mitochondrial complex II of the A. suum adult worm together with the absence of complexes III and IV activities in its respiratory chain, it is a good model to examine the reactive oxygen species production from the mitochondrial complex II.
We have developed a multi-mode integrated transponder with four schemes of modulation and conducted a demonstration test in orbit with a demonstration test model. We have also manufactured a ...qualification test model and completed development as a versatile component for JAXA satellites. The decision has been taken to include the MTP on board various JAXA satellites and it is currently in the manufacturing phase. We will subsequently report on the main functions of the MTP and the results of the demonstration test in orbit.
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