Increased superoxide production during fatigue in the perfused rat diaphragm

This study test the hypothesis that a temporal relationship exists between the production of superoxide anion (O2 −) and the contractile activity of perfused rat diaphragm. O2 − levels were determined minute to minute by measuring the reduction of cytochrome c in the perfusate as the diaphragms were subjected to various levels of contractile activity. After equilibrating at low contractile rates (one 500 ms 80 Hz train/min), diaphragms were fatigued by increasing their contractile activity for 5 min (one 500 ms 80 Hz train/s) and then allowed to recover for 30 min (one 500 ms 80 Hz train/min). During equilibration, diaphragms did not produce O2 − above the background level measured in the presence of superoxide dismutase (SOD). Within the first minute of fatigue-inducing stimulation, however, the rate of O2 − production increased to 0.70 ± 0.17 nmol/min and remained elevated until the recovery period when production returned towards baseline. SOD blocked this stimulation-related increase of O2 −. Tension ...