APPS November 2002 Meeting Abstract 125


Graham D. Lamb, Giuseppe S. Posterino, Department of Zoology, La Trobe University, Vic., 3086.

Reactive oxygen species are generated in skeletal muscle1, but there is considerable uncertainty about what effects oxidation has on the various steps in excitation-contraction (E-C) coupling and what role if any it plays in muscle fatigue. Here, we used mechanically-skinned fibres from fast-twitch (extensor digitorum longus, EDL) and slow-twitch (soleus) muscles of the rat. Electrical stimulation was used to trigger action potential-induced twitch responses2. The Ca2+-sensitivity and maximum force production of the contractile apparatus was examined by direct activation with heavily-buffered Ca2+ solutions. Strong reducing conditions had little if any effect on the properties of the contractile apparatus or on twitch responses, showing that it is not necessary to have some level of fibre oxidation for normal muscle function. In EDL fibres oxidised by H2O2 or dithiodipyridine, exposure to the endogenous reductant, glutathione (GSH), caused a paradoxical increase in the Ca2+-sensitivity of the contractile apparatus that was reversed by exposure to dithiothreitol or longer exposure to GSH. This effect, which did not occur in slow-twitch fibres, could contribute to the well-known phenomenon of post-tetanic potentiation. Oxidants also increased Ca2+-sensitivity by another mechanism which depended on fibre activation. Prolonged exposure to H2O2 however reduced both sensitivity and maximum force. The amount of Ca2+ released from the sarcoplasmic reticulum in a twitch response was not altered by H2O2 treatment, even though such treatment greatly potentiated the sensitivity to Ca2+-induced Ca2+ release3. Strong oxidative treatment was also found to reduce or abolish twitch responses by interfering in some way with activation of the voltage sensors. These findings explain how H2O2 treatment initially potentiates, then reduces, twitch and sub-maximal tetanic force responses in intact fibres4 and show how oxidation can have both beneficial and deleterious effects in skeletal muscle.

(1) Reid MB. Journal of Applied Physiology. 2001;90:724-731.

(2) Posterino GS, Lamb GD, Stephenson DG. Journal of Physiology. 2000;527:131-137.

(3) Plant DR, Lynch GS, Williams DA. Journal of Physiology. 2002;539:883-891.

(4) Andrade FH, Reid MB, Allen DG, Westerblad H. Journal of Physiology. 1998;509:565-575.

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