骨骼肌细胞内的线粒体位于肌肉收缩装置之间(纤维间线粒体,IFM)或细胞膜下方(肌膜线粒体,SSM),IFM和SSM之间报告了一些结构和功能差异。然而,最近的3D成像研究表明,线粒体特别集中在嵌入肌膜沟的毛细血管附近,而不是靠近肌膜本身(血管旁线粒体,PVM)。评估毛细管与毛细管的影响接近肌膜,我们比较了位于嵌入毛细血管(PVM)外侧的骨骼肌线粒体的结构和功能,与肉瘤相邻,但不在PVM池(SSM)中或散布在肉瘤(IFM)之间。通过3D电子显微镜结合机器学习分割评估线粒体形态和相互作用,而线粒体能量转换是通过线粒体膜电位的双光子显微镜评估的,内容,钙,活的NADH氧化还原和通量,完整的细胞。在结构上,尽管PVM和SSM同样大于IFM,PVM更大,与IFM和SSM相比,更圆,与相邻线粒体的物理连接更多。功能上,与SSM和IFM相比,PVM具有相似或更大的基础NADH通量,分别,尽管氧化的NADH池和更大的膜电位,表示PVM中电子传输链的更大激活。一起,这些数据表明,与单纯的肌膜相比,靠近毛细血管对骨骼肌静息线粒体能量转换和分布的影响更大。要点:毛细血管对骨骼肌线粒体能量转换的影响大于肌膜。血管旁线粒体更大,线粒体外膜与邻近的线粒体有更多的联系。纤维间线粒体更长,与其他细胞器(即肌浆网和脂滴)的接触部位更大。血管旁线粒体在静息时比纤维间线粒体具有更大的氧化磷酸化激活,虽然它不受钙的调节。
Mitochondria within skeletal muscle cells are located either between the muscle contractile apparatus (interfibrillar mitochondria, IFM) or beneath the cell membrane (subsarcolemmal mitochondria, SSM), with several structural and functional differences reported between IFM and SSM. However, recent 3D imaging studies demonstrate that mitochondria are particularly concentrated in the proximity of capillaries embedded in sarcolemmal grooves rather than in proximity to the
sarcolemma itself (paravascular mitochondria, PVM). To evaluate the impact of capillary vs. sarcolemmal proximity, we compared the structure and function of skeletal muscle mitochondria located either lateral to embedded capillaries (PVM), adjacent to the
sarcolemma but not in PVM pools (SSM) or interspersed between sarcomeres (IFM). Mitochondrial morphology and interactions were assessed by 3D electron microscopy coupled with machine learning segmentation, whereas mitochondrial energy conversion was assessed by two-photon microscopy of mitochondrial membrane potential, content, calcium, NADH redox and flux in live, intact cells. Structurally, although PVM and SSM were similarly larger than IFM, PVM were larger, rounder and had more physical connections to neighbouring mitochondria compared to both IFM and SSM. Functionally, PVM had similar or greater basal NADH flux compared to SSM and IFM, respectively, despite a more oxidized NADH pool and a greater membrane potential, signifying a greater activation of the electron transport chain in PVM. Together, these data indicate that proximity to capillaries has a greater impact on resting mitochondrial energy conversion and distribution in skeletal muscle than the
sarcolemma alone. KEY POINTS: Capillaries have a greater impact on mitochondrial energy conversion in skeletal muscle than the
sarcolemma. Paravascular mitochondria are larger, and the outer mitochondrial membrane is more connected with neighbouring mitochondria. Interfibrillar mitochondria are longer and have greater contact sites with other organelles (i.e. sarcoplasmic reticulum and lipid droplets). Paravascular mitochondria have greater activation of oxidative phosphorylation than interfibrillar mitochondria at rest, although this is not regulated by calcium.