Fatigue‐induced change in T‐system excitability and its major cause in rat fast‐twitch skeletal muscle in vivo
Fatigue‐induced change in T‐system excitability and its major cause in rat fast‐twitch skeletal muscle in vivo
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疲劳引起的大鼠快肌骨骼肌T系统兴奋性变化及其主要原因
DOI：
10.1113/jp279574
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发表时间：
2020
期刊：
影响因子：
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通讯作者：
Wada Masanobu
中科院分区：
文献类型：
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作者：
Watanabe Daiki;Wada Masanobu
利用机械剥皮的大鼠肌肉纤维，我们研究了(I)高强度收缩后横管系统(T系统)的兴奋性，以及(Ii)疲劳引起T系统兴奋性改变的机制。使用由T系统Na+-K+-ATPase高度调节的皮肤纤维估计的T系统兴奋性在肌肉收缩后降低，但通过二硫苏糖醇处理完全恢复。肌肉收缩后，整个肌肉中Na+-K+-ATPase的S-谷胱甘肽基化增加，在静息但未刺激的纤维中也发生在非常低的ATP条件下。结论：大强度运动后T系统的兴奋性降低，至少部分是由于Na+-K+-ATPase的谷胱甘肽基化，而收缩引起的ATP抑制可能会增强T系统的兴奋性。本研究的目的是研究在体骨骼肌收缩后横管系统(T系统)的兴奋性，以及Na+-K+-ATPase的谷胱甘肽基化的贡献。在去除肌膜但T系统仍起作用的情况下，通过测量机械剥皮纤维中双动作电位所需的重启时间(RP)来评估T系统的兴奋性。部分去极化条件下的RP高度依赖于Na+-K+-ATPase的功能。对大鼠腓肠肌(GAS)进行反复收缩，直至肌力降至初始力的∼50%，然后迅速切取肌肉，用于去皮纤维和生化实验。部分去极化状态下刺激纤维的Rp增加(5.9ms±1.0ms，P<0.05)。8.0ms±1.5ms(刺激时)，但用二硫苏糖醇序贯治疗可逆转这一升高。在极低的≤(1 MM)条件下，仅在氧化谷胱甘肽(GSSG)处理的情况下，静息肌肉中的皮肤纤维表现出较慢的激活速度，而GSSG处理后的刺激纤维中的RP没有改变。与此相一致的是，Na+-K+-α酶的β2-和ATPase亚基在刺激时比在静息状态下更多地谷胱甘肽基化。这些结果提示：(1)收缩过程中T系统兴奋性降低，部分原因是T系统Na~+-K~+-ATPase的下调；(2)S谷胱甘肽基化导致疲劳引起的T系统Na~+-K~+-ATPase功能下降；(3)收缩过程中的ATP抑制可能增强T系统Na~+-K~+-ATPase的谷胱甘肽基化。
Key pointsUsing mechanically skinned rat muscle fibres, we investigated (i) transverse tubular‐system (T‐system) excitability after high‐intensity contractions, and (ii) the mechanisms underlying the fatigue‐induced alteration of the T‐system excitability.T‐system excitability estimated by using skinned fibres, which is highly regulated by T‐system Na+‐K+‐ATPase, was decreased after muscle contractions, but was fully restored by treatment with dithiothreitol.TheS‐glutathionylation of Na+–K+‐ATPase in whole muscle was increased after muscle contractions and also occurred under very low ATP conditions in rested but not stimulated fibres.In conclusion, T‐system excitability was decreased after high‐intensity exercise due at least in part to theS‐glutathionylation of Na+–K+‐ATPase, which may be enhanced by contraction‐induced ATP depression.AbstractThe purpose of this study was to investigate transverse tubular system (T‐system) excitability after skeletal muscle contractionsin vivo, and the contribution ofS‐glutathionylation of Na+–K+‐ATPase. T‐system excitability was estimated by measuring the repriming period (RP) required for double action potentials in mechanically skinned fibres where the sarcolemma was removed but the T‐system still functioned. The RP under partially depolarized conditions was highly dependent on the function of Na+–K+‐ATPase. Rat gastrocnemius (GAS) muscles were subjected to repetitive contractions until the force was decreased to ∼50% of initial force, and then the muscles were very quickly excised and used for skinned fibre and biochemical experiments. The RP under partially depolarized conditions was increased in stimulated fibres (5.9 ± 1.0 ms in restedvs. 8.0 ± 1.5 ms in stimulated); however, this increase in RP was reversed by sequential treatment with dithiothreitol. The skinned fibres from rested muscles exhibited slower repriming only when treated with oxidized glutathione (GSSG) under very low ATP (≤1 mm) conditions, whereas the RP in stimulated fibres was not altered after GSSG treatment without ATP. In line with this, the α2‐ and β‐subunits of Na+–K+‐ATPase were moreS‐glutathionylated in stimulated than in rested muscles. These results suggest that (i) T‐system excitability is decreased during contractions, in part due to a downregulation of T‐system Na+–K+‐ATPase, (ii)S‐glutathionylation contributes to the fatigue‐induced decline of the T‐system Na+–K+‐ATPase function, and (iii) ATP depression throughout contractions may enhanceS‐glutathionylation of T‐system Na+–K+‐ATPase.