Several studies show that dietary nitrate enhances exercise performance, presumably by increasing muscle blood flow and improving oxygen utilization. These effects are likely mediated by nitrate metabolites, including nitrite and nitric oxide (NO). However, the mechanisms of nitrate production, storage, and metabolism to nitrite and NO in skeletal muscle cells are still unclear. We hypothesized that exogenous nitrate can be taken up and metabolized to nitrite/NO inside the skeletal muscle. We found rapid uptake of exogeneous nitrate in both myoblasts and myotubes, increasing nitrite levels in myotubes, but not myoblasts. During differentiation we found increased expression of molybdenum containing proteins, such as xanthine oxidoreductase (XOR) and the mitochondrial amidoxime-reducing component (MARC); nitrate and nitrite reductases. Sialin, a known nitrate transporter, was detected in myoblasts; nitrate uptake decreased after sialin knockdown. Inhibition of chloride channel 1 (CLC1) also led to significantly decreased uptake of nitrate. Addition of exogenous nitrite, which resulted in higher intracellular nitrite levels, increased intracellular cGMP levels in myotubes. In summary, our results demonstrate for the first time the presence of the nitrate/nitrite/NO pathway in skeletal muscle cells, namely the existence of strong uptake of exogenous nitrate into cells and conversion of intracellular nitrate to nitrite and NO. Our results further support our previously formulated hypothesis about the importance of the nitrate to nitrite to NO intrinsic reduction pathways in skeletal muscles, which likely contributes to improved exercise tolerance after nitrate ingestion.

中文翻译：

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人体骨骼肌细胞培养物中的硝酸盐吸收和代谢。


多项研究表明，饮食中的硝酸盐可能通过增加肌肉血流量和提高氧气利用率来增强运动表现。这些影响可能是由硝酸盐代谢物介导的，包括亚硝酸盐和一氧化氮 (NO)。然而，骨骼肌细胞中硝酸盐产生、储存以及代谢为亚硝酸盐和一氧化氮的机制仍不清楚。我们假设外源性硝酸盐可以在骨骼肌内被吸收并代谢为亚硝酸盐/NO。我们发现成肌细胞和肌管中外源硝酸盐的快速摄取，增加了肌管中的亚硝酸盐水平，但不增加成肌细胞中的亚硝酸盐水平。在分化过程中，我们发现含钼蛋白质的表达增加，例如黄嘌呤氧化还原酶（XOR）和线粒体偕胺肟还原成分（MARC）；硝酸盐和亚硝酸盐还原酶。在成肌细胞中检测到了唾液酸（Sialin），一种已知的硝酸盐转运蛋白；唾液酸蛋白敲低后硝酸盐吸收减少。抑制氯离子通道 1 (CLC1) 也会导致硝酸盐的摄取显着减少。添加外源亚硝酸盐会导致细胞内亚硝酸盐水平升高，从而增加肌管中的细胞内 cGMP 水平。总之，我们的结果首次证明骨骼肌细胞中存在硝酸盐/亚硝酸盐/NO途径，即细胞对外源硝酸盐的强烈摄取以及细胞内硝酸盐转化为亚硝酸盐和NO的存在。我们的结果进一步支持了我们之前提出的假设，即骨骼肌中硝酸盐、亚硝酸盐、一氧化氮内在还原途径的重要性，这可能有助于提高摄入硝酸盐后的运动耐量。