The general purpose of this proposal is to evaluate aspects of adenine nucleotide metabolism in skeletal muscle. The influence of exercise, the differences between skeletal muscle fiber types, the influence of exercise training and the physiological significance of certain metabolic pathways will be assessed. Although muscle contractions establish a high rate of ATP hydrolysis, the concomitant acceleration in the rate of ADP phosphorylation tends to limit the decrease in ATP concentration. During intense exercise conditions, however, a reduction of the total adenine nucleotide pool (TAN = ATP + ADP + AMP) can occur. This is due to degradative reactions leading to IMP, nucleoside and purine production. The quantity and nature of the products are probably not the same in the different skeletal muscle fiber types. The extent of adenine nucleotide degradation during muscle stimulation, the differences between muscle fiber types and the dependence on the metabolic stress will be determined using an isolated perfused rat hindlimb preparation. Assays and purification of adenine nucleotides, purine nucleosides and purines will be performed using high performance liquid chromatography. Recovery of TAN following exercise via de novo synthesis and/or purine salvage pathways, factors that influence the synthesis pathways and their interaction will be assessed in the different muscle fiber types. The impact of muscle adaptations, induced by exercise training, on the degradation/synthesis processes will be assessed. The activity of key pathway enzymes will be determined under optimal conditions in vitro and related to the degradation and synthesis processes determined previously for each fiber type. The metabolic and functional consequences of AMP deaminase will be determined by inhibiting IMP production during moderate to intense exercise. These unique studies will provide fundamental information important for the understanding of adenine nucleotide metabolism in the various fiber types of normal muscle. This information, in turn, should greatly increase our understanding of abnormalities in adenine nucleotide metabolism found in certain myopathies, and the potential consequences of related muscle enzyme deficiencies.
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