Local injection of BaCl2 is an established model of acute injury to study the regeneration of skeletal muscle. However, the mechanism by which BaCl2 causes muscle injury is unresolved. Because Ba2+ inhibits K+ channels, we hypothesized that BaCl2 induces myofiber depolarization leading to Ca2+ overload, proteolysis, and membrane disruption. While BaCl2 spares resident satellite cells, its effect on other tissue components integral to contractile function has not been defined. We therefore asked whether motor nerves and microvessels, which control and supply myofibers, are injured by BaCl2 treatment. The intact extensor digitorum longus (EDL) muscle was isolated from male mice (aged 3–4 months) and irrigated with physiological salt solution (PSS) at 37 °C. Myofiber membrane potential (Vm) was recorded using sharp microelectrodes while intracellular calcium concentration ([Ca2+]i) was evaluated with Fura 2 dye. Isometric force production of EDL was measured in situ, proteolytic activity was quantified by calpain degradation of αII-spectrin, and membrane disruption was marked by nuclear staining with propidium iodide (PI). To test for effects on motor nerves and microvessels, tibialis anterior or gluteus maximus muscles were injected with 1.2% BaCl2 (50–75 μL) in vivo followed by immunostaining to evaluate the integrity of respective tissue elements post injury. Data were analyzed using Students t test and analysis of variance with P ≤ 0.05 considered statistically significant. Addition of 1.2% BaCl2 to PSS depolarized myofibers from − 79 ± 3 mV to − 17 ± 7 mV with a corresponding rise in [Ca2+]i; isometric force transiently increased from 7.4 ± 0.1 g to 11.1 ± 0.4 g. Following 1 h of BaCl2 exposure, 92 ± 3% of myonuclei stained with PI (vs. 8 ± 3% in controls) with enhanced cleavage of αII-spectrin. Eliminating Ca2+ from PSS prevented the rise in [Ca2+]i and ameliorated myonuclear staining with PI during BaCl2 exposure. Motor axons and capillary networks appeared fragmented within 24 h following injection of 1.2% BaCl2 and morphological integrity deteriorated through 72 h. BaCl2 injures myofibers through depolarization of the sarcolemma, causing Ca2+ overload with transient contraction, leading to proteolysis and membrane rupture. Motor innervation and capillarity appear disrupted concomitant with myofiber damage, further compromising muscle integrity.

中文翻译：

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氯化钡通过钙诱导的蛋白水解作用以及运动神经和微血管的碎裂来伤害肌纤维。

局部注射BaCl2是研究骨骼肌再生的急性损伤模型。但是，BaCl 2引起肌肉损伤的机理尚未阐明。因为Ba2 +抑制了K +通道，所以我们假设BaCl2诱导肌纤维去极化，导致Ca2 +超载，蛋白水解和膜破裂。尽管BaCl2保留了常驻卫星细胞，但尚未确定其对收缩功能必不可少的其他组织成分的作用。因此，我们问BaCl2处理是否会损伤控制和供应肌纤维的运动神经和微血管。从雄性小鼠（3-4月龄）中分离完整的指伸伸肌（EDL）肌肉，并在37°C下用生理盐溶液（PSS）进行灌溉。使用锋利的微电极记录肌纤维膜电位（Vm），同时用Fura 2染料评估细胞内钙浓度（[Ca2 +] i）。在原位测量EDL的等轴测力产生，通过钙蛋白酶降解αII-血影蛋白定量蛋白水解活性，并通过碘化丙啶（PI）核染色标记膜破坏。为了测试对运动神经和微血管的影响，在胫骨前肌或臀大肌体内注入1.2％BaCl2（50–75μL），然后进行免疫染色以评估损伤后各个组织元素的完整性。使用Student t检验分析数据，并认为P≤0.05的差异具有统计学意义。向PSS中添加1.2％BaCl2使去极化的肌纤维从-79±3 mV增至-17±7 mV，[Ca2 +] i相应增加；等轴测力从7.4±0.1 g瞬时增加到11.1±0.4 g。在BaCl2暴露1小时后，有92±3％的肌核被PI染色（与对照组的8±3％相比），αII-血影蛋白的切割增强。从PSS中消除Ca2 +可以防止[Ca2 +] i的升高，并改善BaCl2暴露期间PI引起的肌核染色。注射1.2％BaCl2后24小时内，运动轴突和毛细血管网络出现碎片，并且在72小时内形态完整性恶化。BaCl2通过肌膜去极化使肌纤维受损，导致Ca2 +超负荷并发生短暂收缩，从而导致蛋白水解和膜破裂。运动神经支配和毛细血管扩张伴随着肌纤维损伤而出现，进一步损害了肌肉的完整性。在BaCl2暴露1小时后，有92±3％的肌核被PI染色（与对照组的8±3％相比），αII-血影蛋白的切割增强。从PSS中消除Ca2 +可以防止[Ca2 +] i的升高，并改善BaCl2暴露期间PI引起的肌核染色。注射1.2％BaCl2后24小时内，运动轴突和毛细血管网络出现碎片，并且在72小时内形态完整性恶化。BaCl2通过肌膜去极化使肌纤维受损，导致Ca2 +超负荷并发生短暂收缩，从而导致蛋白水解和膜破裂。运动神经支配和毛细血管扩张伴随着肌纤维损伤而出现，进一步损害了肌肉的完整性。在BaCl2暴露1小时后，有92±3％的肌核被PI染色（与对照组的8±3％相比），αII-血影蛋白的切割增强。从PSS中消除Ca2 +可以防止[Ca2 +] i的升高，并改善BaCl2暴露期间PI引起的肌核染色。注射1.2％BaCl2后24小时内，运动轴突和毛细血管网络出现碎片，并且在72小时内形态完整性恶化。BaCl2通过肌膜去极化使肌纤维受损，导致Ca2 +超负荷并发生短暂收缩，从而导致蛋白水解和膜破裂。运动神经支配和毛细血管扩张伴随着肌纤维损伤而出现，进一步损害了肌肉的完整性。从PSS中消除Ca2 +可以防止[Ca2 +] i的升高，并改善BaCl2暴露期间PI引起的肌核染色。注射1.2％BaCl2后24小时内，运动轴突和毛细血管网络出现碎片，并且在72小时内形态完整性恶化。BaCl2通过肌膜去极化使肌纤维受损，导致Ca2 +超负荷并发生短暂收缩，从而导致蛋白水解和膜破裂。运动神经支配和毛细血管扩张伴随着肌纤维损伤而出现，进一步损害了肌肉的完整性。从PSS中消除Ca2 +可以防止[Ca2 +] i的升高，并改善BaCl2暴露期间PI引起的肌核染色。注射1.2％BaCl2后24小时内，运动轴突和毛细血管网络出现碎片，并且在72小时内形态完整性恶化。BaCl2通过肌膜去极化使肌纤维受损，导致Ca2 +超负荷并发生短暂收缩，从而导致蛋白水解和膜破裂。运动神经支配和毛细血管扩张伴随着肌纤维损伤而出现，进一步损害了肌肉的完整性。BaCl2通过肌膜去极化使肌纤维受损，导致Ca2 +超负荷并发生短暂收缩，从而导致蛋白水解和膜破裂。运动神经支配和毛细血管扩张伴随着肌纤维损伤而出现，进一步损害了肌肉的完整性。BaCl2通过肌膜的去极化作用损伤肌纤维，导致Ca2 +超负荷并短暂收缩，从而导致蛋白水解和膜破裂。运动神经支配和毛细血管扩张伴随着肌纤维损伤而出现，进一步损害了肌肉的完整性。