The aim of this study was to investigate the effects of an enzymatic removal of glycogen on excitation–contraction coupling in mechanically skinned fibres of rat fast-twitch muscles, with a focus on the changes in the function of Na⁺–K⁺-pump and ryanodine receptor (RyR). Glycogen present in the skinned fibres and binding to microsomes was removed using glucoamylase (GA). Exposure of whole muscle to 20 U mL⁻¹ GA for 6 min resulted in a 72% decrease in the glycogen content. Six minutes of GA treatment led to an 18 and a 22% reduction in depolarization- and action potential-induced forces in the skinned fibres, respectively. There was a minor but statistically significant increase in the repriming period, most likely because of an impairment of the Na⁺–K⁺-pump function. GA treatment exerted no effect on the maximum Ca²⁺ release rate from the RyR in the microsomes and the myofibrillar Ca²⁺ sensitivity in the skinned fibres. These results indicate that reduced glycogen per se can decrease muscle performance due to the impairment of SR Ca²⁺ release and suggest that although Na⁺–K⁺-pump function is adversely affected by reduced glycogen, the extent of the impairment is not sufficient to reduce Ca²⁺ release from the sarcoplasmic reticulum. This study provides direct evidence that glycogen above a certain amount is required for the preservation of the functional events preceding Ca²⁺ release from the sarcoplasmic reticulum.

中文翻译：

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减少的肌糖原对大鼠快支肌兴奋-收缩偶联的影响：糖原去除研究。

这项研究的目的是研究酶促去除糖原对大鼠快肌的机械表皮纤维中兴奋-收缩偶联的影响，重点是Na ⁺ -K ^+-泵和ryanodine受体（RyR）。使用葡糖淀粉酶（GA）可以去除皮肤纤维中存在的糖原并与微粒体结合。将全肌肉暴露于20 U mL ^-1 GA 6分钟会导致糖原含量降低72％。六分钟的GA处理可使蒙皮纤维中的去极化和动作电位诱导的力分别降低18％和22％。恢复期有轻微但统计学上显着的增加，最可能是由于Na的损伤⁺ –K ^+-泵功能。GA处理对微粒体中RyR的最大Ca ²⁺释放速率和皮肤纤维中的肌原纤维Ca ²⁺敏感性没有影响。这些结果表明，糖原本身降低会由于SR Ca ²⁺释放受损而降低肌肉性能，并表明尽管Na ⁺ -K ^+-泵功能受到糖原降低的不利影响，但损害的程度不足以减少从肌质网释放的Ca ²⁺。这项研究提供了直接的证据表明，糖原必须高于一定量才能保持Ca ²⁺之前的功能事件 从肌质网释放。