Abstract
Muscle fatigue may be due to a failure in excitation‐contraction coupling or an increase of ATP by products and NO. E‐c coupling alterations occur earlier and metabolic alterations take place later. We investigated these possibilities in frog skeletal muscle by continuous high frequency stimulation and different periods of repetitively stimulations. We judged the extent of e‐c or metabolic possibilities by releasing Ca2+ with 5 mM caffeine prior and immediately after fatigue.Continuously 60 Hz electric stimulations produced a force dropped to 0.33 ± 0.05 SD the control tetanus force, within a few seconds. The ratio of caffeine force development after and before fatigue was 1.02 ± 0.24 SD. This indicated that the interaction of myosin with actin was not impaired. After repetitive stimulation, the force dropped to 0.85 ± 0.04 SD (6 tetani) and 0.65± 0.11 SD (24 tetani) the control tetanus. Here, the ratio of caffeine force after and before fatigue development was 0.75 ± 0.3 SD. The concentration of caffeine used was the same as before therefore the acto‐myosin interaction was impaired during prolonged repetitive stimulations. The two types of fatigue take place.
Published Version
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