Effects of age on mechanical and electrical performance of rat myocardium

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. 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.