Abstract

In its second messenger role in skeletal muscle, calcium coordinates the function of muscle (contractile activity) with its overall energetics, thereby controlling the provision of ATP in a time of need. Not only is AtP required for crossbridge turnover in the myofibrils, but it is also needed for the maintenance of ion pumps, nuclear activity, and so forth. When oxygen is limiting, the sustained contractions of both fast and slow muscle (after the immediate burst of activity) is primarily supported by glycogenolysis and the glycolytic pathway (anaerobic). Calcium is important to this process, and the compartmentation of the glycogen particle and some of the enzymes associated with the glycolytic pathway in the terminal cisternae of the sarcoplasmic reticulum ensures that the provision of glucose-6-phosphate to the glycolytic pathway for the generation of the needed ATP proceeds rapidly. The activation of phosphorylase and glycogenolysis by calcium-troponin-C is another example of the tight control of cellular energetics deemed possible by compartmentation within the cell. The regulation by calcium, therefore, is only dependent on the diffusion of calcum rather than diffusion of substrate. Verf.-Referat (gekuerzt)