Intracellular muscle free amino acids—their measurement and function

It is hoped that this presentation will focus attention and research upon the need to correlate nutrition more directly with the biochemistry of the individual tissue and cell.Such a focus, which is so essential to modem nutrition, must be considered as a way toward a more complete understanding of the dynamic system which forms the whole animal.Muscle tissue is by far the most abundant cellular tissue in the body and is relatively uniform as to cellular composition.Profound biochemical changes in muscle are known to accompany electrolyte disorders, circulatory disturbances and nutritional deficiencies.In addition, morphological changes occur in certain muscle disorders and in generalized diseases.Biochemical and morphological studies of muscle tissue in man under various physiological and pathological conditions have proved to be of great value in clinical research and in the diagnosis of various diseases (Bergstrom, 1962;Edwards et al. 1973;Bergstrom, 1975). Sampling and analytical techniquesExtensive studies of normal and pathological muscle metabolism require a simple method for muscle sampling.Percutaneous needle biopsy was introduced by Duchenne as early as 1868 for the investigation of patients with muscular dystrophy (Duchenne, 1868).The method seems, however, to have been little used until 1957, when it was suggested that percutaneous needle biopsy should be used for the study of muscle electrolytes in man in conjunction with neutron activation analysis (Reiffel & Stone, 1957).Bergstrom (1962), using a new biopsy needle and a 5 mm incision in the thigh made under local anaesthesia, obtained samples of quadriceps of femoris muscle amounting to 30-100 mg of tissue.This method of sampling is rapid and only slightly traumatic and can therefore be repeated several times in the same individual.Muscle function is usually little impaired immediately after the biopsy, as shown by the fact that subjects have been able to continue to compete in an 85 km cross-country ski race after several such biopsies (Bergstrom et al. 1973).Further improvements of the muscle biopsy technique have been made by Edwards et al. (1980).With the use of modem microanalytical techniques the biopsy sample can be analysed for water (Bergstrom, 1962), electrolytes (Bergstrom & Friden, 1975), lipids (Bergstrom, 1962;Froberg, 1973) and free amino acids (Bergstrom et al. 1974(Bergstrom et al. , 1976)), as well as adenine nucleotides, creatine phosphate, creatine, glycolytic intermediates, glycogen and various enzymes (Harris et al. 1974).The calculation of extra-and intracellular water is based on the chloride method,