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Review
. 2024 Mar;24(3):84-90.
doi: 10.1016/j.bjae.2023.12.003. Epub 2024 Jan 22.

Recent advances in skeletal muscle physiology

V Kaura  1 , P M Hopkins  1
Affiliations
Review

Recent advances in skeletal muscle physiology

V Kaura et al. BJA Educ. 2024 Mar.
No abstract available

Keywords: excitation–contraction coupling; malignant hyperthermia; muscle fatigue; sarcopenia; skeletal muscle.

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Conflict of interest statement

PMH is the Editor-in-Chief of BJA Open and an editorial board member of the BJA. VK was a previous BJA editorial fellow in 2021–2022.

Figures

Fig 1
Fig 1
The Goldman–Hodgkin–Katz voltage equation is used to calculate the membrane potential in a multi-ion system and can help estimate the sarcolemma membrane potential. It is a modification of the Nernst equation described previously and can be used to determine the effect on the membrane potential of altering the intra- or extracellular concentrations of several different ions.
Fig 2
Fig 2
Key structures involved in excitation–contraction coupling and store-operated Ca2+ entry (SOCE). A change in the t-tubular membrane potential induces a conformational change in the Cav1.1 subunit of the Cav1.1 complex whereby the II–III loop directly interacts and activates the type 1 ryanodine receptor (RYR1); this subsequently releases sarcoplasmic reticulum (SR) Ca2+, thus permitting muscle contraction. The SR contains approximately 1 mM of free Ca2+ with further releasable Ca2+ stores bound within calsequestrin. Any excess cytosolic Ca2+ is actively pumped back into the SR by the sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) pump. This together with RYR1 deactivation allows muscle relaxation. SH3 and cysteine-rich domain 3 (STAC3) helps chaperone Cav1.1 to the sarcolemma membrane and stabilises the Cav1.1–RYR1 coupling. The STIM1–ORAI interaction facilitates SOCE—other proteins such as TRPC3/6 may also contribute to SOCE, Ca2+ entry at rest (RCaE), or both. STIM1 functions as the SR Ca2+ sensor with ORAI forming a complex that permits extracellular Ca2+ into the cell. Inset: A skeletal muscle triad consists of a t-tubule sandwiched between two SR terminal cisternae; this ensures the proteins involved in EC coupling are closely apposed, thereby allowing the rapid transduction of the electrical signal into mechanical contraction (adapted from OpenStax, Skeletal Muscle, used under CC-BY-4.0). STIM1, stromal-interacting molecule 1; TRPC, transient receptor potential canonical.
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