Proteins in the Denervated Muscle, Changes in their Quantity, Properties and Metabolism

Abstract

Loss of muscle weight and finally complete degenerative dedifferentation of muscle tissue are the most prominent results of interrupting the connection between the muscle and the nervous system. Nevertheless, chemical investigations performed towards the end of the 19th Century analyzing quantitative changes in the denervated muscle were concentrated on study of glycogen, creatine and creatinephosphate. This is all the more surprising since, at that time, it was believed that muscle proteins play a substantial role in muscular work (Pflüger). First reports dealing with protein changes in denervated muscles were by Steyrer (1903) and Grund (1912). The former described changes in the myosin: myogen ratio, while the latter pointed out the marked decrease of phosphorus-free protein. The methods of investigating properties of muscle proteins were at that time very imperfect and it is therefore difficult to evaluate these two findings from the point of view of contemporary knowledge. The first exact data were published from a physiological laboratory, when Langley and Kato (1915) determined the gradient of denervation atrophy on the basis of changes in wet muscle weight. By 1921 Lipschütz and Audova showed that tenotomy as well as denervation leads to a gradual loss of muscle proteins. In spite of effort continuing up to the present it has not been possible to differentiate exactly between these two kinds of atrophy. The above investigations of atrophic Muscles were made at the time of fundamental discoveries by Fletscher and Hopkins in 1907 and Meyerhof in 1919. These authors reported an increase of lactic acid in muscle following contraction in a nitrogen atmosphere and concluded that glycolysis serves as source of energy for contraction. During the course of the following years, therefore the interest of biochemists should focus on muscle contraction energetics, an area of study concerning the basic function of muscle. Systematic investigation of the denervated muscle was thus not undertaken until 20 years after the report of Langley and Kato, by Hines and Knowlton (1933). These authors studied rather the physiological characteristics of the muscle undergoing atrophy, such as loss of protein mass, the course of atrophy in various types of muscles, changes in different animals species, etc.