HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: 586/8/2203    most recent jphysiol.2007.150516v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Murphy, R. M. Articles by Lamb, G. D. Search for Related Content PubMed PubMed Citation Articles by Murphy, R. M. Articles by Lamb, G. D. Related Collections Skeletal Muscle and Exercise

¹ Department of Zoology, La Trobe University, Melbourne, Victoria, Australia

Studies on intact muscle fibres indicate that reactive oxygen species (ROS) produced during muscle activity, or applied exogenously, can cause decreased force responses primarily by reducing the Ca²⁺ sensitivity of the contractile apparatus. Identification of the molecular basis of this effect is complicated by the fact that studies on skinned muscle fibres in general have not observed reduced contractile Ca²⁺ sensitivity when applying ROS, predominantly H₂O₂. Here, using skinned fibres from rat extensor digitorum longus (EDL) and soleus muscle, it is shown that although H₂O₂ ( 100 µM) has little effect by itself, when added in the presence of myoglobin it causes marked reduction in the Ca²⁺ sensitivity of the contractile apparatus, probably due to production of hydroxyl radicals (OH). Maximum force production is also reduced, but only with larger or more prolonged treatments. The effects are not prevented by tempol, a potent superoxide scavenger. Dithiotreitol (DTT) produces little reversal of the sensitivity change if applied afterwards, but it does substantially reverse all the changes if applied before the fibre undergoes an activation sequence. When glutathione (GSH, 5 mM) is present, exposure of EDL fibres to H₂O₂ and myoglobin causes an increase in Ca²⁺ sensitivity, with longer treatments causing a subsequent decrease, whereas in soleus fibres it causes only decreases in sensitivity and maximum force. The increased Ca²⁺ sensitivity in EDL fibres is evidently due to the summed actions of (i) a potentiating effect of glutathionylation, which can be reversed by DTT and only occurs in fast-twitch fibres, and (ii) a less reversible reduction in sensitivity. Western blotting showed that reductions in Ca²⁺ sensitivity were not due to loss of troponin-C. The present findings help provide a mechanistic basis for diverse findings on the effects of ROS in muscle fibres and implicate OH radicals and glutathione as likely mediators of the effects.

(Received 23 December 2007; accepted after revision 25 February 2008; first published online 28 February 2008)
Corresponding author G. D. Lamb: Department of Zoology, La Trobe University, Melbourne 3086, Victoria, Australia. Email: g.lamb{at}latrobe.edu.au