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This Article Full Text Full Text (PDF) Supplemental Data All Versions of this Article: 564/3/723    most recent jphysiol.2005.083030v1 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 HighWire Citing Articles via Google Scholar Google Scholar Articles by Gueguen, N. Articles by Herpin, P. Search for Related Content PubMed PubMed Citation Articles by Gueguen, N. Articles by Herpin, P.

¹ INRA, Unité Mixte de Recherche Système d'Elevage Nutrition Animale et Humaine, Domaine de la Prise, 35590 Saint-Gilles, France

Mitochondrial respiration rates and their regulation by ADP, AMP and creatine, were studied at different free Ca²⁺ concentrations (0.1 versus 0.4 µM) on permeabilized fibre bundles of rabbit skeletal muscles differing in their myosin heavy chain profiles. Four fibre bundle types were obtained: pure types I and IIx, and mixed types IIax (approximately 50% IIa and 50% IIx fibres) and IIb+ (60% IIb fibres, plus IIx and IIa). At rest, pure type I fibres displayed a much higher apparent K_m for ADP (212 µM) than IIx fibres (8 µM). Within the IIax and IIb+ mixed fibre bundle types, two K^ADP_m values were observed (70 µM and 5 µM). Comparison between pure IIx and mixed types indicates that the intermediate K_m of 70 µM most probably corresponds to the mitochondrial affinity for ADP in IIa fibres, the lowest K_m for ADP (5 µM) corresponding to IIx and IIb types. Activation of mitochondrial creatine and adenylate kinase reactions stimulated mitochondrial respiration only in type I and IIax fibre bundles, indicating an efficient coupling between both kinases and ADP rephosphorylation in type I and, likely, IIa fibres, since no effect was observed in pure IIx fibres. Following Ca²⁺-induced activation of myosin-ATPase, an increase in mitochondrial sensitivity to ADP of 45% and 250% was observed in type IIax and I bundles, respectively, an effect mostly prevented by addition of vanadate, an inhibitor of myosin-ATPase. Ca²⁺-induced activation of myosin-ATPase also prevented the stimulation of respiration rates by creatine and AMP in I and IIax bundles. In addition to differential regulation of mitochondrial respiration and energy transfer systems at rest in I and IIa versus IIx and IIb muscle fibres, our results indicate a regulation of phosphotransfer systems by Ca²⁺ via the stimulation of myosin-ATPases in type I and IIa fibres of rabbit muscles.

(Received 11 January 2005; accepted after revision 18 February 2005; first published online 24 February 2005)
Corresponding author L. Lefaucheur: INRA, Unité Mixte de Recherche SENAH, Domaine de la Prise, 35590 Saint-Gilles, France. Email: louis.lefaucheur{at}rennes.inra.fr

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