Reactive oxygen in skeletal muscle. II. Extracellular release of free radicals.
We have tested the hypothesis that diaphragm muscle fibers release superoxide anion radicals (O2-.) into the extracellular space. Fiber bundles were isolated from rat diaphragm and incubated in Krebs-Ringer solution containing cytochrome c (10(-5) M), a standard assay for O2-.. Bundles were either passive or active, i.e., directly stimulated to contract rhythmically. After 1 h, absorbance of reduced cytochrome c in the incubation medium was measured at 550 nm. Absorbance was greater in medium exposed to passive muscle than in medium without muscle (P < 0.01), indicating O2-. release by passive muscle. Absorbance was greater in medium exposed to active muscle than in that exposed to passive muscle (P < 0.01), an increase inhibited by superoxide dismutase (10(3) U/ml). Active bundles fatigued; bundles developing the lowest final stresses produced the greatest absorbance increases (P < 0.001), suggesting that the magnitude of fatigue was inversely related to O2-. release. We conclude that O2-. is released by diaphragm myocytes into the interstitium and surrounding medium, a process accelerated by fatiguing muscular contractions.
Reid
M B
MB
Department of Medicine, Baylor College of Medicine, Houston, Texas 77030.
Shoji
T
T
Moody
M R
MR
Entman
M L
ML
D000818:Animals; D003574:Cytochrome c Group / Q000378:metabolism; D004558:Electric Stimulation; D005110:Extracellular Space / Q000378:metabolism*; D005609:Free Radicals / Q000378:metabolism; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D009132:Muscles / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017382:Reactive Oxygen Species / Q000378:metabolism*; D012132:Respiratory Muscles / Q000502:physiology; D014969:Xanthine Oxidase / Q000378:metabolism
D003574:Cytochrome c Group; D005609:Free Radicals; D017382:Reactive Oxygen Species; D014969:Xanthine Oxidase