| dc.description.abstract | Skeletal muscle fatigue is typically thought to involve accumulated lactic acid, increased Pi concentration,
decreased muscle glycogen, and/or increased levels of oxygen free radicals, but a clear cause of
muscle fatigue has remained elusive. Additionally, it is unclear if these factors affect type I (slow
oxidative) and type II (A: fast oxidative, B: fast glycolytic) fibers equally. Recent evidence suggests
that increasing extracellular K+ concentration reduces the contractile function of isolated rat soleus
muscle, while moderately elevated H+ levels provide a protective effect on contractile force. To study
the combined effects of mild acidification with elevated K+ on muscle contraction and fatigue, we
stimulated isolated Xenopus laevis gastrocnemius muscles to complete exhaustion following 30 minutes
of pre-incubation with one of the following solutions: normal amphibian Ringer’s (pH = 7.45),
amphibian Ringer’s with elevated (4mM) K+, amphibian Ringer’s with decreased pH (20mM L-lactic
acid), and amphibian Ringer’s with both elevated K+ and H+. Following pre-incubation in their respective
solutions, muscles were mounted on a force transducer and stimulated with supramaximal
stimuli at 60 Hz until completely fatigued. Force of contraction, muscle kinetics (latency, contraction
time, and ½-relaxation time), and time to exhaustion were measured. | en_US |
