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Abstract

Muscular contraction stems from a sliding movement of thick and thin filaments relative to each other. These filaments run parallel to the direction of the muscle fibre. The thin filaments, which issue from the Z-membrane into the sarcomere, consist of 60% actin, and 40% regulator proteins (tropomyosin and troponin). The thick filament consists almost entirely of myosin. The two types of filaments form on overlapping region, the length of which depends on the degree of shortening of the muscle. The mechanical work which is produced by the muscle during shortening is produced by the so-called myosin cross-bridges, which appear to attach to actin, change their angle, and then detach in a cyclical “rowing-boat” manner. During such a cycle, ATP is split to ADP and inorganic phosphate, and therefore the production of mechanical work is based on the interaction of actin and myosin at the expense of chemical energy, which is supplied in the form of ATP. In the last 20 years, the structure of the involved proteins and their aggregation and ordering in the filaments has been widely investigated. Similarly, the rough nature of the electromechanical coupling process has been explained. i. e. the sequence of events which is necessary to activate a resting muscle into contraction via a neural impulse. At the present time, much interest is concentrated on the kinetic analysis of ATP hydrolysis and the modification of certain reaction steps by actin. From experiments of this sort, a more detailed and propound understanding of the nature of the mechanochemical energy coupling mechanism can be expected.