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Cyclic stretch reduces myofibrillar protein synthesis despite increases in FAK and anabolic signalling in L6 cells
Muscle protein synthesis is increased after exercise, but evidence is now accruing that during muscular activity it is suppressed. In life, muscles are subjected to shortening forces due to contraction, but may also be subject to stretching forces during lengthening. It would be biologically ineffic...
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Published in: | The Journal of physiology 2009-07, Vol.587 (14), p.3719-3727 |
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Main Authors: | , , , , , , , |
Format: | Article |
Language: | English |
Subjects: | |
Citations: | Items that this one cites Items that cite this one |
Online Access: | Get full text |
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Summary: | Muscle protein synthesis is increased after exercise, but evidence is now accruing that during muscular activity it is suppressed.
In life, muscles are subjected to shortening forces due to contraction, but may also be subject to stretching forces during
lengthening. It would be biologically inefficient if contraction and stretch have different effects on muscle protein turnover,
but little is known about the metabolic effects of stretch. To investigate this, we assessed myofibrillar and sarcoplasmic
protein synthesis (MPS, SPS, respectively) by incorporation of [1- 13 C]proline (using gas chromatographyâmass spectrometry) and anabolic signalling (by phospho-immunoblotting and kinase assays)
in cultured L6 skeletal muscle cells during 30 min of cyclic stretch and over 30 min intervals for up to 120 min afterwards.
SPS was unaffected, whereas MPS was suppressed by 40 ± 0.03% during stretch, before returning to basal rates by 90â20 min
afterwards. Paradoxically, stretch stimulated anabolic signalling with peak values after 2â30 min: e.g. focal adhesion kinase
(FAK Tyr576/577; +28 ± 6%), protein kinase B activity (Akt; +113 ± 31%), p70S6K1 (ribosomal S6 kinase Thr389; 25 ± 5%), 4E
binding protein 1 (4EBP1 Thr37/46; 14 ± 3%), eukaryotic elongation factor 2 (eEF2 Thr56; â47 ± 4%), extracellular regulated
protein kinase 1/2 (ERK1/2 Tyr202/204; +65% ± 9%), eukaryotic initiation factor 2α (eIF2α Ser51; â20 ± 5%, P < 0.05) and eukaryotic initiation factor 4E (eIF4E Ser209; +33 ± 10%, P < 0.05). After stretch, except for Akt activity, stimulatory phosphorylations were sustained: e.g. FAK (+26 ± 11%) for â¥30
min, eEF2 for â¥60 min (peak â45 ± 4%), 4EBP1 for â¥90 min (+33 ± 5%), and p70S6K1 remained elevated throughout (peak +64 ±
7%). Adenosine monophosphate-activated protein kinase (AMPK) phosphorylation was unchanged throughout. We report for the first
time that acute cyclic stretch specifically suppresses MPS, despite increases in activity/phosphorylation of elements thought
to increase anabolism. |
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ISSN: | 0022-3751 1469-7793 |
DOI: | 10.1113/jphysiol.2009.169854 |