Effects of cytoplasmic free Mg²⁺ buffering on skeletal muscle fatigue in intact single mouse muscle fibers.

Authors

Daiki Watanabe, Nathaniel J Andrews, Ihtisham A Rana, Aditya N Brahmbhatt, Christopher G R Perry, Arthur J Cheng

Published in

American journal of physiology. Cell physiology. Sep 29, 2026. Epub Sep 29, 2026.

Abstract

Changes in cytoplasmic free Mg²⁺ concentration ([Mg²⁺]_cyto) might play a key role in regulating skeletal muscle function. Mag-indo-1, a fluorescence dye that specifically binds to Mg²⁺, can be used both to detect and buffer [Mg²⁺]_cyto. In this study, we hypothesized that buffering the fatigue-induced elevations in [Mg²⁺]_cyto would mitigate fatigue by preserving sarcoplasmic reticulum (SR) Ca²⁺ release. Intact fibers were isolated from the flexor digitorum brevis muscle, and loaded with varying concentration of Mag-indo-1-AM. The fibers were repeatedly stimulated at 70 Hz for 300 msec every 2 sec for 100 contractions (fatiguing stimulation: FS). To examine the relationship between fatigue and Mg²⁺ buffering, we compared the force produced during the final contraction of FS with the amount of Mag-indo-1 loading before FS (Fatigue-Mg²⁺ buffer relationship). Fatigue-Mg²⁺ buffer relationship exhibited an inverted U-shaped curve: fatigue resistance improved when [Mag-indo-1] increased up to an optimal level, but declined when [Mag-indo-1] became excessive. Therefore, the fibers were classified into three groups: underloaded, optimal-loaded and overloaded groups. Caffeine treatment immediately after FS significantly enhanced force recovery in the underloaded group, reaching a level comparable to that of caffeine-treated, optimal-loaded group. Furthermore, mitochondrial coupled respiration was impaired, and proton leak was enhanced in the presence of nM level Mag-indo-1. These results suggest that elevated [Mg²⁺]_cyto contributes to muscle fatigue due to impairments of SR Ca²⁺ release. Conversely, excessive buffering of [Mg²⁺]_cyto may also exacerbate muscle fatigue, indicating that a proper [Mg²⁺]_cyto balance is critical for maintaining fatigue resistance.

PMID:
42809442
Bibliographic data and abstract were imported from PubMed on 30 Sep 2026.

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