Effects Of Electric Stimulus On M Waves And Force In Rat Fast-and Slow-Twitch Muscles Incubated Under Normoxia And Hypoxia

Objective:Both muscle mechanics and electric activity characteristic changed evidently during the process of skeletal muscle fatigue.The investigation on isolated skeletal muscle under hypoxia incubation was less.The propose of this study was to explore the changes of electrophysiology and force on slow-twitch fibres(SOL) and fast-twitch fibres(EDL) handled by electric stimulus of various frequencies and oxygen incubation,and the possible mechanism further.Methods:All experiments were carried out using 4-week-old male Wistar rats weighing 60-75 g.After incubated in K-R buffer isolated muscles were mounted through tendons for isometric contractions exposed to electric stimulus of various frequencies.M waves and force were simultaneous recorded.Preparations were freezed immediately after experiment to test the biochemical indexes.Conclusion:1.Progressive electric stimulus resulted in the decline of area and amplitude,frequency was higher,the changes more obvious;and synergistic effect disappeared;The influence of oxygen content on the areas of M waves was different according to the type of muscle fiber and frequency of stimulus;Under tetanic stimulation,the extent of decline was similar incubated in normoxia between SOL and EDL,but was different in hypoxia(p<0.05);2.In normoxia group,the changes of force were similar between EDL and SOL;In hypoxia group,the capability of resisting fatigue of SOL was better than EDL,frequency was higher,the changes more obvious;3、Area of M wave was positive correlation to force with regardless of SOL and EDL,hyperxia and normoxia;But there was a little difference between normoxia and hypoxia groups,the former SOL exceeded EDL,the latter was contrary.Both SOL and EDL,the enzyme activity of Na+-K+-ATPase was highest under 20Hz;4.To SOL,the enzyme was activated easily under normoxia incubation, but was contrary to EDL;The enzyme activity of Ca2+-ATPase was suppressed under hypoxia incubation,but to some degree,increasing frequency of stimulation could against the suppression according the type of muscle fiber;5.The relation among Na+-K+-ATPase activity and M waves or force was not always coincidence,Particularly complicated under tetanus stimulus. Similarity,there was no some relation among Ca2+-ATPase activity and M wave or force.