Store-Operated Ca2+ Entry in Skeletal Muscle Contributes to the Increase in Body Temperature during Exertional Stress

Abstract

Exertional heat stroke (HS) is a hyperthermic crisis triggered by an excessive accumulation of Ca2+ in skeletal muscle fibers. We demonstrated that exercise leads to the formation of calcium entry units (CEUs), which are intracellular junctions that reduce muscle fatigue by promoting the recovery of extracellular Ca2+ via store-operated Ca2+ entry (SOCE). Here, we tested the hypothesis that exercise-induced assembly of CEUs may increase the risk of HS when physical activity is performed in adverse environmental conditions (high temperature and humidity). Adult mice were: (a) first, divided into three experimental groups: control, trained-1 month (voluntary running in wheel cages), and acutely exercised-1 h (incremental treadmill run); and (b) then subjected to an exertional stress (ES) protocol, a treadmill run in an environmental chamber at 34°C and 40% humidity. The internal temperature of the mice at the end of the ES was higher in both pre-exercised groups. During an ES ex-vivo protocol, extensor digitorum longus(EDL) muscles from the trained-1 month and exercised-1 h mice generated greater basal tension than in the control and were those that contained a greater number of CEUs, assessed by electron microscopy. The data collected suggest that the entry of Ca2+ from extracellular space via CEUs could contribute to exertional HS when exercise is performed in adverse environmental conditions.

Proteomic reference map for sarcopenia research: mass spectrometric identification of key muscle proteins located in the sarcomere, cytoskeleton and the extracellular matrix

“… 43-45 , 113 In analogy, fast versus slow troponin isoforms were identified in the actin-containing thin filaments. 113 , 11 4 This shows that the presented analysis pipeline is suitable for studying myofiber type shifting during aging. 30 Crucial extra-sarcomeric cytoskeletal proteins were identified in skeletal muscles, including the central cytolinker plectin, 115 and members of costameres such as alpha7/beta1-integrin, 116 and alpha/beta-dystroglycan in conjunction with its membrane cytoskeletal anchor named dystrophin.…”

“… 117 , 118 This would enable the in-depth analysis of alterations in the levels of lateral force transmission through costameric structures in aged skeletal muscles. Since the extracellular matrix is a crucial structural component of muscles, 11 9 and majorly involved in reactive myofibrosis in neuromuscular diseases, 120 , 121 it is encouraging that representative markers of the basal lamina, endomysium, perimysium, epimysium and tendon could be detected by proteomics in crude muscle tissue extracts. In conclusion, the mass spectrometric screening of senescent mouse muscles has been successfully applied to establish a proteomic reference map for future sarcopenia research.…”

Searching for Mechanisms Underlying the Assembly of Calcium Entry Units: The Role of Temperature and pH

“…Note the bump-phase (indicatedby arrows in Figure 6 A and Figure 7 A), which was previously characterized in two papers by Michelucci and colleagues as the phase of activation of SOCE [ 81 , 82 ]. To demonstrate whether the increased fatigue resistance registered in EDL muscles exercised ex vivo at 36 °C (pH 7.4) and at 7.2 (25 °C) was due to increased Ca 2+ entry via SOCE, we performed parallel experiments conducted using either: (i) a Ca 2+ -free solution, in which Ca 2+ was replaced by an equimolar concentration of Mg 2+ ; or (ii) a Ca 2+ -containing solution supplemented with 10 μM BTP-2 ( Figure 6 C and Figure 7 C), an established inhibitor of SOCE [ 77 , 79 , 90 , 91 , 92 ]. These experiments indicated that the enhanced fatigue resistance of EDL muscles exercised ex vivo at 36 °C (pH 7.4) and at pH 7.2 (25 °C) containing ex vivo assembled CEUs ( Figure 4 and Figure 5 ) was effectively due to the entry of extracellular Ca 2+ via SOCE, as inhibition of Ca 2+ entry results in faster decay of contractile force ( Figure 6 C and Figure 7 C).…”

“…Muscle activity generates heat: the temperature of human skeletal muscle can increase from 33 °C up to 39 °C during exercise [ 94 ], raising the possibility that heat-induced Ca 2+ influx via SOCE could play a role in skeletal muscle physiology. We have recently shown that exercise-dependent assembly of CEUs could contribute to exertional heat stroke when exercise is performed in adverse environmental conditions [ 92 ]. In the present study, the assembly of functional CEUs was favored by physiological temperature, when compared to 25 °C.…”

Ablation of Calsequestrin-1, Ca2+ unbalance, and susceptibility to heat stroke

“…Hence, Ca 2+ entry plays a role in contracture of biopsies and MH susceptibility. We have also recently showed that assembly of CEUs during exercise contributes to the increase in body temperature during exertional stress ( Girolami et al, 2022 ). One puzzling question to answer in our future work would be: the constitutively active SOCE in Casq1-null fibers may contribute to the MH/HS susceptibility of these mice?…”