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The importance of limitations in aerobic metabolism, glycolysis, and membrane excitability for the development of high-frequency fatigue in isolated rat soleus muscle

journal contribution
posted on 2024-08-20, 05:36 authored by Kate Murphy, T Clausen
We investigated the role of limitations in aerobic metabolism, glycolysis, and membrane excitability for development of high-frequency fatigue in isolated rat soleus muscle. Muscles mounted on force transducers were incubated in buffer bubbled with 5% CO2 and either 95% O2 (oxygenated) or 95% N2 (anoxic) and stimulated at 60 Hz continuously for 30–120 s or intermittently for 120 s. Cyanide (2 mM) and 2-deoxyglucose (10 mM) were used to inhibit aerobic metabolism and both glycolysis and aerobic metabolism, respectively. Excitability was reduced by carbacholine (10 μM), a nicotinic ACh receptor agonist, or ouabain (10 μM), an Na+-K+ pump inhibitor. Membrane excitability was measured by recording M waves. Intracellular Na+ and K+ contents and membrane potentials were measured by flame photometry and microelectrodes, respectively. During 120 s of continuous stimulation, oxygenated and anoxic muscles showed the same force loss. In oxygenated muscles, cyanide did not alter force loss for up to 90 s, whereas 2-deoxyglucose increased force loss (by 19–69%; P < 0.01) from 14 s of stimulation. In oxygenated muscles, 60 s of stimulation reduced force, M wave area, and amplitude by 70–90% ( P < 0.001). Carbacholine or ouabain increased intracellular Na+ content ( P < 0.001), induced a 7- to 8-mV membrane depolarization ( P < 0.001), and accelerated the rate of force loss (by 250–414%) during 30 s of stimulation ( P < 0.001). Similar effects were seen with intermittent stimulation. In conclusion, limitations in glycolysis and subsequently also in aerobic metabolism, as well as membrane excitability but not aerobic metabolism alone, appear to play an important role in the development of high-frequency fatigue in isolated rat soleus muscle.

History

Journal

American Journal of Physiology-Regulatory, Integrative and Comparative Physiology

Volume

292

Pagination

R2001-R2011

Location

United States

ISSN

0363-6119

eISSN

1522-1490

Language

en

Publication classification

C1.1 Refereed article in a scholarly journal

Issue

5

Publisher

American Physiological Society