Section of Physiology, Division of Pulmonary, Critical Care & Sleep Medicine, Department of Medicine, University of California, San Diego, California.
J Appl Physiol (1985). 2022 Apr 1;132(4):1041-1053. doi: 10.1152/japplphysiol.00861.2021. Epub 2022 Mar 3.
One of the most important cytosolic Ca buffers present in mouse fast-twitch myofibers, but not in human myofibers, is parvalbumin (PV). Previous work using conventional PV gene () knockout (PV-KO) mice suggests that lifelong ablation increases fatigue resistance, possibly due to compensations in mitochondrial volume. In this work, ablation was induced only in adult mice (PV-KO), and contractile and cytosolic Ca responses during fatigue were studied in isolated muscle and intact single myofibers. Results were compared with control littermates (PV-Ctr). We hypothesized that the reduced myofiber cytosolic Ca buffering developed only in adult PV-KO mice leads to a larger cytosolic free Ca concentration ([Ca]) during repetitive contractions, increasing myofiber fatigue resistance. Extensor digitorum longus (EDL) muscles from PV-KO mice had higher force in unfused stimulations (∼50%, < 0.05) and slowed relaxation (∼46% higher relaxation time, < 0.05) versus PV-Ctr, but muscle fatigue resistance or fatigue-induced changes in relaxation were not different between genotypes ( > 0.05). In intact single myofibers from flexor digitorum brevis (FDB) muscles, basal and tetanic [Ca] during fatiguing contractions were higher in PV-KO ( < 0.05), accompanied by a greater slowing in estimated sarcoplasmic reticulum (SR) Ca-pumping versus PV-Ctr myofibers (∼84% reduction, < 0.05), but myofiber fatigue resistance was not different between genotypes ( > 0.05). Our results demonstrate that although the estimated SR Ca uptake was accelerated in PV-KO, the total energy demand by the major energy consumers in myofibers, the cross-bridges, and SR Ca ATPase were not altered enough to affect the energy supply for contractions, and therefore fatigue resistance remained unaffected. Parvalbumin (PV) is a cytosolic Ca buffer that is present in mouse myofibers but not in human muscle. We show that inducible knockout of leads to increases in myofiber cytosolic free Ca concentrations and slowing of Ca pumping during fatigue versus control mice. However, ablation does not interfere with fatigue-induced slowing in relaxation or fatigue resistance. These data support the use of mouse muscle as a suitable model to investigate human muscle fatigue.
在快速收缩肌纤维中，一种存在于鼠但不存在于人肌肉中的重要胞浆 Ca 缓冲蛋白是肌钙蛋白 I（PV）。使用传统的 PV 基因敲除（PV-KO）小鼠的先前工作表明，终生缺失会增加抗疲劳能力，这可能是由于线粒体体积的代偿。在这项工作中，仅在成年小鼠（PV-KO）中诱导缺失，并在分离的肌肉和完整的单个肌纤维中研究疲劳期间的收缩和胞浆 Ca 反应。结果与对照同窝仔（PV-Ctr）进行了比较。我们假设，只有在成年 PV-KO 小鼠中，减少的肌纤维胞浆 Ca 缓冲作用的发展会导致重复收缩期间更大的胞浆游离 Ca 浓度 ([Ca])，从而增加肌纤维的抗疲劳能力。与 PV-Ctr 相比，来自 PV-KO 小鼠的伸趾长肌（EDL）肌肉在未融合刺激时具有更高的力（约 50%，<0.05）和更慢的松弛（约 46%更高的松弛时间，<0.05），但两种基因型之间的肌肉抗疲劳能力或疲劳诱导的松弛变化没有差异（>0.05）。在来自屈趾短肌（FDB）肌肉的完整单个肌纤维中，疲劳收缩期间的基础和强直 [Ca] 在 PV-KO 中更高（<0.05），同时与 PV-Ctr 肌纤维相比，估计的肌浆网（SR）Ca 泵的速度减慢（约 84%，<0.05），但两种基因型之间的肌纤维抗疲劳能力没有差异（>0.05）。我们的结果表明，尽管在 PV-KO 中估计的 SR Ca 摄取加速，但肌纤维中主要能量消耗者，即横桥和 SR Ca-ATP 酶的总能量需求没有改变到足以影响收缩的能量供应，因此抗疲劳能力保持不变。肌钙蛋白 I（PV）是一种存在于鼠肌纤维但不存在于人肌肉中的胞浆 Ca 缓冲蛋白。我们表明，诱导性敲除导致肌纤维胞浆游离 Ca 浓度增加，并在疲劳时与对照小鼠相比，Ca 泵的速度减慢。然而，缺失不会干扰疲劳诱导的松弛减慢或抗疲劳能力。这些数据支持将小鼠肌肉用作研究人类肌肉疲劳的合适模型。
