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Departments of 1 Physiology and 2 Movement Sciences, Maastricht University, 6200 MD Maastricht, The Netherlands
Creatine kinase (CK)
forms a small family of isoenzymes playing an important role in
maintaining the concentration of ATP and ADP in muscle cells. To
delineate the impact of a lack of CK activity, we studied contractile
performance during a single maximal tetanic contraction and during 12 repeated tetanic contractions of intact dorsal flexors of CK knockout
(CK
/
) mice. To investigate the effect on ATP
regeneration, muscular high-energy phosphate content was determined at
rest, immediately after the contraction series, and after a 60-s
recovery period. Maximal torque of the dorsal flexors was significantly
lower in CK
/
mice than in wild-type animals, i.e.,
23.7 ± 5.1 and 33.3 ± 6.8 mN · m · g
1 wet wt, respectively. Lower
muscle ATP (20.1 ± 1.4 in CK
/
vs. 28.0 ± 2.1 µmol/g dry wt in controls) and higher IMP (1.2 ± 0.5 in
CK
/
vs. 0.3 ± 0.1 µmol/g dry wt in controls)
levels at the onset of contraction may contribute to the declined
contractility in CK
/
mice. In contrast to wild-type
muscles, ATP levels could not be maintained during the series of 12 tetanic contractions of dorsal flexors of CK
/
mice and
dropped to 15.5 ± 2.4 µmol/g dry wt. The significant increase
in tissue IMP (2.4 ± 1.1 µmol/g dry wt) content after the
contraction series indicates that ATP regeneration through adenylate
kinase was not capable of fully compensating for the lack of CK. ATP
regeneration via the adenylate kinase pathway is a likely cause of
reduced basal adenine nucleotide levels in CK
/
mice.
skeletal muscle; creatine kinase deficiency; repeated contractions
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