METHODS: We determined the free Ca2+ redistribution during a 2 s 60 Hz tetanic stimulation in the sarcoplasmic reticulum, cytosol, and mitochondria. Via a reaction-diffusion Ca2+ model, we quantitatively evaluated mitochondrial uptake and storage capacity requirements to compensate for PV lack and analyzed possible extracellular export.
RESULTS: [Ca2+]mito during tetanic stimulation is greater in knock-out (KO) (1362 ± 392 nM) than in wild-type (WT) (855 ± 392 nM), p < 0.05. Under the assumption of a non-linear intramitochondrial buffering, the model predicts an accumulation of 725 μmoles/L fiber (buffering ratio 1:11 000) in KO, much higher than in WT (137 μmoles/L fiber, ratio 1:4500). The required transport rate via mitochondrial calcium uniporter (MCU) reaches 3 mM/s, compatible with available literature. TEM images of calcium entry units and Mn2+ quenching showed a greater capacity of store-operated calcium entry in KO compared to WT. However, levels of [Ca2+]cyto during tetanic stimulation were not modulated to variations of extracellular calcium.
CONCLUSIONS: The model-based analysis of experimentally determined calcium distribution during tetanic stimulation showed that mitochondria can act as a buffer to compensate for the lack of PV. This result contributes to a better understanding of mitochondria\'s role in modulating [Ca2+]cyto in skeletal muscle fibers.
方法:我们确定了肌浆网中2s60Hz强直刺激期间的游离Ca2再分布,胞质溶胶,和线粒体.通过反应扩散Ca2+模型,我们定量评估了线粒体摄取和储存能力需求,以弥补PV缺乏,并分析了可能的细胞外输出.
结果:[Ca2+]mito在强直刺激期间的敲除(KO)(1362±392nM)大于野生型(WT)(855±392nM),p<0.05。在非线性线粒体内缓冲的假设下,该模型预测在KO中积累725μmoles/L纤维(缓冲比1:11000),远高于WT(137μmoles/L纤维,比率1:4500)。通过线粒体钙单质转运蛋白(MCU)所需的转运速率达到3mM/s,与现有文献兼容。钙进入单元和Mn2淬灭的TEM图像显示,与WT相比,KO中存储操作的钙进入能力更高。然而,强直性刺激期间[Ca2]细胞的水平不受细胞外钙变化的调节。
结论:对强直性刺激过程中实验确定的钙分布的基于模型的分析表明,线粒体可以充当缓冲剂来补偿PV的缺乏。这一结果有助于更好地理解线粒体在调节骨骼肌纤维[Ca2+]细胞中的作用。