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1 Department of Pediatrics, Magee-Womens Research Institute, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15213; 2 Department of Cell Biology and Histology, University of Nijmegen, Nijmegen, The Netherlands; and 3 Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213
Creatine kinase (CK) provides
ATP buffering in skeletal muscle and is expressed as 1)
cytosolic myofibrillar CK (M-CK) and 2) sarcomeric
mitochondrial CK (ScCKmit) isoforms that differ in their subcellular
localization. The diaphragm (Dia) expresses both M-CK and ScCKmit in
abundance. We compared the power and work output of 1) control
CK-sufficient (Ctl), 2) M-CK-deficient [M-CK(
/
)], 3) ScCKmit-deficient
[ScCKmit(
/
)], and 4) combined M-CK/ScCKmit-deficient null mutant [CK(
/
)]
Dia during repetitive isotonic activations to determine the effect of
CK phenotype on Dia function. Maximum power was obtained at ~0.4
tetanic force in all groups. M-CK(
/
) and
ScCKmit(
/
) Dia were able to sustain power and work output
at Ctl levels during repetitive isotonic activation (75 Hz, 330-ms
duration repeated each second at 0.4 tetanic force load), and the
duration of sustained Dia shortening was 67 ± 4 s in
M-CK(
/
), 60 ± 4 s in ScCKmit(
/
), and 62 ± 5 s in Ctl Dia. In contrast, CK(
/
) Dia power and work
declined acutely and failed to sustain shortening altogether by
40 ± 6 s. We conclude that Dia power and work output are
not absolutely dependent on the presence of either M-CK or ScCKmit,
whereas the complete absence of CK acutely impairs Dia shortening
capacity during repetitive activation.
respiratory muscle; fatigue; myosin heavy chain
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