FOG Fibres — The Most Adaptable Muscle Fibres
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In Chap. 5 we investigated the metabolic changes in muscle fibres under changing conditions. Summarizing the effects of all experiments, one can state that metabolic changes occur predominantly in FOG fibres: After acute hypoxia an increased oxidative activity of FOG fibres was measured, caused by the increased mitochondrial respiration. Diabetes induced a shift to glycolysis in FOG fibres. This was interpreted as a reaction to oxidative stress, changed motoric activity or neuropathy. In diabetic muscles the percentage of FOG fibres decreased to the same amount to which the percentage of FG fibres increased. The same effect was observed in several muscles after treatment of rats with Ginkgo biloba extract and during ageing. We can conclude that FOG fibres change their metabolism as long as they convert into FG fibres. In this way FOG fibres, FOG I as well as FOG II fibres are the most adaptable fibres. That may be caused by their metabolic equipment. FOG fibres are metabolically variable; they have high oxidative as well as glycolytic capacity. This is in contrast to SO and FG fibres where the oxidative and glycolytic capacities are reciprocal. SO and FG fibres prefer one pathway (oxidative or glycolytic, respectively) of energy metabolism; FOG fibres can use both pathways equally. Although each muscle fibre can, to a certain extent, shift between both metabolic pathways, the metabolic shift is possible in FOG rather than in the other fibres. It was shown that under changing experimental conditions, the metabolic shift can finally result in the transition of FOG fibres to FG fibres.