https://www.selleckchem.com/products/azd3965.html We describe here reliable histochemical and immunohistochemical techniques to visualize mitochondria and respiratory chain dysfunction in tissue sections. These morphological methods have been widely used for years, and yet remain relevant to obtain insight into the pathogenesis of mitochondrial diseases. Today, mitochondrial medicine is changing rapidly and genetic information plays an increasing role in the diagnostic process, owing to advances in next-generation sequencing. However, tissue analysis and morphological categorization remain essential, especially when genetic abnormalities of unknown significance might complicate a diagnostic odyssey. Furthermore, tissue assessment is an essential step in laboratory investigation using animal or cell models, in order to assess the distribution, severity, and/or progression of the disease, and to evaluate the effects of possible treatments. Optimized and reproducible staining and imaging methodology are the key elements for accurate tissue assessment. When these methods are used properly and integrated with wisely chosen genetic and biochemical approaches, powerful information can be obtained about the structure and function of mitochondria in both animal model systems and human patients. While the described protocols refer to skeletal muscle and brain mitochondria, the methods described can be applied to any tissue type. © 2020 Elsevier Inc. All rights reserved.Assessment of the mitochondrial membrane potential (Δψ) in living cells, although not trivial, can be used to estimate mitochondrial bioenergetic state. For this purpose, fluorescent lipophilic cations are broadly applied. These cations enter cells and accumulate primarily in the mitochondrial matrix in a Δψ-dependent manner. Here, we describe the use of the cations tetramethylrhodamine methyl ester (TMRM) and rhodamine 123 (Rhod123) for semi-quantitative Δψ analysis in living mammalian cells. Two different str