Mitochondrial metabolic function assessed in vivo and in vitro

Purpose of review: Mitochondrial content and function vary across species, tissue types, and lifespan. Alterations in skeletal muscle mitochondrial function have been reported to occur in aging and in many other pathological conditions. This review focuses on the state of the art in-vivo and in-vitro methodologies for assessment of muscle mitochondrial function. Recent findings: Classic studies of isolated mitochondria have measured function from maximal respiratory capacity. These fundamental methods have recently been substantially improved and novel approaches to assess mitochondrial functions in vitro have emerged. Noninvasive methods based on magnetic resonance spectroscopy and near-infrared spectroscopy permit in-vivo assessment of mitochondrial function and are rapidly becoming more accessible to many investigators. Moreover, it is now possible to gather information on regulation of mitochondrial content by measuring the in-vivo synthesis rate of individual mitochondrial proteins. Summary: High-resolution respirometry has emerged as a powerful tool for in-vitro measurements of mitochondrial function in isolated mitochondria and permeabilized fibers. Direct measurements of adenosine triphosphate production are possible by bioluminescence. Mechanistic data provided by these methods is further complimented by in-vivo assessment using magnetic resonance spectroscopy and near-infrared spectroscopy and the translational rate of gene transcripts.