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 (+/-SOD) fell to 12% of the control value during the fatigue-inducing stimulation. During recovery the contractile response returned to 51% of control, indicating long-lasting effects on the contractile machinery. SOD did not limit fatigue or improve recovery, probably because it is a large protein that cannot cross cell membranes and protect the cells by scavenging O2- at its site of production.
Kolbeck
R C
RC
Department of Medicine, Medical College of Georgia, Augusta 30912, USA.
She
Z W
ZW
Callahan
L A
LA
Nosek
T M
TM
D000818:Animals; D003964:Diaphragm / Q000378:metabolism* / Q000502:physiology; D009119:Muscle Contraction / Q000502:physiology; D018763:Muscle Fatigue / Q000502:physiology*; D009924:Organ Culture Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley; D013481:Superoxides / Q000378:metabolism*
D013481:Superoxides