effects of physical training on the heart
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Publication
Journal: The American journal of physiology
August/10/1983
Abstract
Left ventricular papillary muscles were isolated from male Fischer rats at 3, 6, 12, and 24 mo of age. Mechanical performance and transmembrane action potential characteristics were recorded simultaneously. Contractile protein enzyme activity was determined in the same hearts from which papillary muscles were used for acquisition of mechanical and electrical information. There was an age-related increase in the isometric time to peak tension and time to half relaxation with no age-related change in peak isometric developed tension. Resting tension showed a significant increase at both 12 and 24 mo of age. Although no significant change was noted in peak rate of tension rise (+T') or fall (-T'), there was a significant age-related prolongation in the time to +T' and -T'. Isotonically, peak shortening decreased in 24-mo-old animals. Time to peak shortening increased, whereas peak velocity of muscle shortening decreased from 3 to 24 mo of age. A significant and progressive prolongation was noted in the duration of the transmembrane action potential at 50% and 75% repolarization. In addition an age-related progressive decline was seen in contractile protein enzyme activity. These biochemical and electrophysiological alterations may help to explain the contractile modifications during aging.
Publication
Journal: Journal of Biological Chemistry
October/13/1981
Abstract
The 20,000-dalton light chain of cardiac muscle myosin can be specifically digested and thereby removed from the rest of the myosin molecule by incubation with a myofibrillar protease (Malhotra, A., Huang, S., and Bhan, A. (1979) Biochemistry 18, 461-467). In order to study the effects of phosphorylation of the 20,000-dalton myosin light chain, experiments were carried out with cardiac muscle myosin that was made deficient in this light chain following proteolysis. Both the phosphorylated and unphosphorylated isolated 20,000-dalton myosin light chain of cardiac muscle myosin were found to bind to light chain-deficient myosin. Prior to readdition of the isolated light chains, this light chain-deficient myosin was found to have a higher MgATPase activity in the presence and absence of actin, than native myosin. Binding of the unphosphorylated myosin light chain restored the MgATPase activity of light chain-deficient myosin to that of native cardiac myosin. In contrast, the binding of 2 mol of the previously phosphorylated myosin light chain did not lower the actin-activated MgATPase activity. The results suggest that while phosphorylation of the 20,000-dalton light chain of cardiac muscle myosin is not essential for the actin-activated MgATPase activity, it may have a modulatory role.