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Fibre diversity is an intrinsic property of skeletal muscle. The “knowledge” of a muscle fibre about whether it has to be slow or fast derives from the genetic code. During their lifetime the fibres do not forget their inaugural program, but they can adapt to changed functional conditions by varying their properties. The aim of this review was to characterize the fibre types of rat skeletal muscles from different points of view and to investigate the adaptability of fibre types to altered physiological and pathological conditions. An overview about the different classification systems and their underlying criteria has been given. Studies from literature as well as our own studies revealed that with only one classification system not all aspects of fibre alterations under changed conditions are recognizable. The parallel application of ATPase-fibre typing, the differentiation of myosin isoforms and metabolic fibre typing leads to real muscle analysis. It was shown that the metabolic situation of a given fibre type in heterogeneously composed muscles can be characterized by cytophotometry. This is a method of quantitative histochemistry based on absorbance measurements of the final reaction product of an enzyme reaction in the histological section. The reliability of cytophotometrical data was proved by the strong correlation to biochemically measured enzyme activities. Fibre typing by cytophotometry has been established and described in detail in the present book. The muscle fibres were typed by measurements of the following three enzyme activities in one and the same fibre: myofibrillic adenosine triphosphatase activity as a marker of contractility, glycerol-3-phosphatedehydrogenase as a marker of glycolysis and succinate dehydrogenase as a marker of oxidative metabolism.
KeywordsFibre Type Myosin Isoforms Final Reaction Product Metabolic Situation Fast Myosin Heavy Chain
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