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Contraction-stimulated glucose transport in muscle is controlled by AMPK and mechanical stress but not sarcoplasmatic reticulum Ca(2+) release.

Jensen TE, Sylow L, Rose AJ, Madsen AB, Angin Y, Maarbjerg SJ, Richter EA - Mol Metab (2014)

Bottom Line: The prevailing concept implicates Ca(2+) as a key feed forward regulator of glucose transport with secondary fine-tuning by metabolic feedback signals through proteins such as AMPK.Rather, the glucose transport response is associated with metabolic feedback signals through AMPK, and mechanical stress-activated signals.These results suggest that ATP-turnover and mechanical stress feedback are sufficient to fully increase glucose transport during muscle contraction, and call for a major reconsideration of the established Ca(2+) centric paradigm.

View Article: PubMed Central - PubMed

Affiliation: Section of Molecular Physiology, Department of Nutrition, Exercise and Sports, University of Copenhagen, 2100 Copenhagen, Denmark.

ABSTRACT
Understanding how muscle contraction orchestrates insulin-independent muscle glucose transport may enable development of hyperglycemia-treating drugs. The prevailing concept implicates Ca(2+) as a key feed forward regulator of glucose transport with secondary fine-tuning by metabolic feedback signals through proteins such as AMPK. Here, we demonstrate in incubated mouse muscle that Ca(2+) release is neither sufficient nor strictly necessary to increase glucose transport. Rather, the glucose transport response is associated with metabolic feedback signals through AMPK, and mechanical stress-activated signals. Furthermore, artificial stimulation of AMPK combined with passive stretch of muscle is additive and sufficient to elicit the full contraction glucose transport response. These results suggest that ATP-turnover and mechanical stress feedback are sufficient to fully increase glucose transport during muscle contraction, and call for a major reconsideration of the established Ca(2+) centric paradigm.

No MeSH data available.


Related in: MedlinePlus

Low-intensity electrically-induced contraction-stimulated glucose transport but not Ca2+ release is abolished by myosin ATPase blockade. 2-deoxyglucose (2DG) transport in A) soleus (SOL) and B) extensor digitorum longus (EDL). C) Representative western blots and quantifications in SOL (top) and EDL (bottom). D) AMPK heterotrimer activities in EDL and E) Representative western blots and quantifications of known AMPK substrates TBC1D1 Ser231 and ACC2 Ser212 in EDL. */**/***p < 0.05/0.01/0.001 contraction-effect vs. ctrl or in (B) 0.1% NST vs. 0.3% NST using Tukey's post hoc test, #p < 0.05 contraction-effect 0.3% NST vs. 0.7% NST, ††p < 0.01 ANOVA contraction × inhibitor interaction. n = 6–8. Data are mean ± S.E.M.
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fig5: Low-intensity electrically-induced contraction-stimulated glucose transport but not Ca2+ release is abolished by myosin ATPase blockade. 2-deoxyglucose (2DG) transport in A) soleus (SOL) and B) extensor digitorum longus (EDL). C) Representative western blots and quantifications in SOL (top) and EDL (bottom). D) AMPK heterotrimer activities in EDL and E) Representative western blots and quantifications of known AMPK substrates TBC1D1 Ser231 and ACC2 Ser212 in EDL. */**/***p < 0.05/0.01/0.001 contraction-effect vs. ctrl or in (B) 0.1% NST vs. 0.3% NST using Tukey's post hoc test, #p < 0.05 contraction-effect 0.3% NST vs. 0.7% NST, ††p < 0.01 ANOVA contraction × inhibitor interaction. n = 6–8. Data are mean ± S.E.M.

Mentions: The effect of myosin ATPase inhibition on the electrically stimulated glucose transport-response was highly dependent on the stimulation protocol, ranging from no difference in glucose transport-stimulation when applying the most intense 0.7% NST protocol in EDL to a complete prevention of glucose transport using the mild 0.1% NST protocol in both soleus and EDL muscles (Figure 5A+B). Consistent with our CPA-experiments, the electrically stimulated increases in eEF2 Thr57 phosphorylation were unaffected by myosin ATPase inhibitors whereas the increases in AMPK Thr172 and p38 MAPK Thr180/Tyr182 phosphorylation were markedly blunted by inhibition of contraction by the myosin inhibitors (Figure 5C). No effect of ex vivo contraction or BTS + Bleb was observed for total protein expression (Figure S2A).


Contraction-stimulated glucose transport in muscle is controlled by AMPK and mechanical stress but not sarcoplasmatic reticulum Ca(2+) release.

Jensen TE, Sylow L, Rose AJ, Madsen AB, Angin Y, Maarbjerg SJ, Richter EA - Mol Metab (2014)

Low-intensity electrically-induced contraction-stimulated glucose transport but not Ca2+ release is abolished by myosin ATPase blockade. 2-deoxyglucose (2DG) transport in A) soleus (SOL) and B) extensor digitorum longus (EDL). C) Representative western blots and quantifications in SOL (top) and EDL (bottom). D) AMPK heterotrimer activities in EDL and E) Representative western blots and quantifications of known AMPK substrates TBC1D1 Ser231 and ACC2 Ser212 in EDL. */**/***p < 0.05/0.01/0.001 contraction-effect vs. ctrl or in (B) 0.1% NST vs. 0.3% NST using Tukey's post hoc test, #p < 0.05 contraction-effect 0.3% NST vs. 0.7% NST, ††p < 0.01 ANOVA contraction × inhibitor interaction. n = 6–8. Data are mean ± S.E.M.
© Copyright Policy - CC BY-NC-ND
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getmorefigures.php?uid=PMC4209358&req=5

fig5: Low-intensity electrically-induced contraction-stimulated glucose transport but not Ca2+ release is abolished by myosin ATPase blockade. 2-deoxyglucose (2DG) transport in A) soleus (SOL) and B) extensor digitorum longus (EDL). C) Representative western blots and quantifications in SOL (top) and EDL (bottom). D) AMPK heterotrimer activities in EDL and E) Representative western blots and quantifications of known AMPK substrates TBC1D1 Ser231 and ACC2 Ser212 in EDL. */**/***p < 0.05/0.01/0.001 contraction-effect vs. ctrl or in (B) 0.1% NST vs. 0.3% NST using Tukey's post hoc test, #p < 0.05 contraction-effect 0.3% NST vs. 0.7% NST, ††p < 0.01 ANOVA contraction × inhibitor interaction. n = 6–8. Data are mean ± S.E.M.
Mentions: The effect of myosin ATPase inhibition on the electrically stimulated glucose transport-response was highly dependent on the stimulation protocol, ranging from no difference in glucose transport-stimulation when applying the most intense 0.7% NST protocol in EDL to a complete prevention of glucose transport using the mild 0.1% NST protocol in both soleus and EDL muscles (Figure 5A+B). Consistent with our CPA-experiments, the electrically stimulated increases in eEF2 Thr57 phosphorylation were unaffected by myosin ATPase inhibitors whereas the increases in AMPK Thr172 and p38 MAPK Thr180/Tyr182 phosphorylation were markedly blunted by inhibition of contraction by the myosin inhibitors (Figure 5C). No effect of ex vivo contraction or BTS + Bleb was observed for total protein expression (Figure S2A).

Bottom Line: The prevailing concept implicates Ca(2+) as a key feed forward regulator of glucose transport with secondary fine-tuning by metabolic feedback signals through proteins such as AMPK.Rather, the glucose transport response is associated with metabolic feedback signals through AMPK, and mechanical stress-activated signals.These results suggest that ATP-turnover and mechanical stress feedback are sufficient to fully increase glucose transport during muscle contraction, and call for a major reconsideration of the established Ca(2+) centric paradigm.

View Article: PubMed Central - PubMed

Affiliation: Section of Molecular Physiology, Department of Nutrition, Exercise and Sports, University of Copenhagen, 2100 Copenhagen, Denmark.

ABSTRACT
Understanding how muscle contraction orchestrates insulin-independent muscle glucose transport may enable development of hyperglycemia-treating drugs. The prevailing concept implicates Ca(2+) as a key feed forward regulator of glucose transport with secondary fine-tuning by metabolic feedback signals through proteins such as AMPK. Here, we demonstrate in incubated mouse muscle that Ca(2+) release is neither sufficient nor strictly necessary to increase glucose transport. Rather, the glucose transport response is associated with metabolic feedback signals through AMPK, and mechanical stress-activated signals. Furthermore, artificial stimulation of AMPK combined with passive stretch of muscle is additive and sufficient to elicit the full contraction glucose transport response. These results suggest that ATP-turnover and mechanical stress feedback are sufficient to fully increase glucose transport during muscle contraction, and call for a major reconsideration of the established Ca(2+) centric paradigm.

No MeSH data available.


Related in: MedlinePlus