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Ca 2+ ‐activated myosin‐ATPases, creatine and adenylate kinases regulate mitochondrial function according to myofibre type in rabbit
Author(s) -
Gueguen N.,
Lefaucheur L.,
Ecolan P.,
Fillaut M.,
Herpin P.
Publication year - 2005
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2005.083030
Subject(s) - myosin , adenylate kinase , creatine kinase , atpase , mitochondrion , creatine , vanadate , respiration , medicine , chemistry , endocrinology , biochemistry , biology , enzyme , anatomy
Mitochondrial respiration rates and their regulation by ADP, AMP and creatine, were studied at different free Ca 2+ concentrations (0.1 versus 0.4 μ m ) 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 μ m ) than IIx fibres (8 μ m ). Within the IIax and IIb+ mixed fibre bundle types, two K ADP m values were observed (70 μ m and 5 μ m ). Comparison between pure IIx and mixed types indicates that the intermediate K m of 70 μ m most probably corresponds to the mitochondrial affinity for ADP in IIa fibres, the lowest K m for ADP (5 μ m ) 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 Ca 2+ ‐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. Ca 2+ ‐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 Ca 2+ via the stimulation of myosin‐ATPases in type I and IIa fibres of rabbit muscles.