The force-interval relation in aged hamster heart

This study determined whether aging affects the force-interval relation in cardiac muscle. Isolated left atria from young (60-120 days) and old (> 535 days) adult hamsters were paced at 1 Hz, and effects of interposing test intervals (0.3-600 sec) on the force of a test beat following the interval (force-interval relation) were examined. To quantify differences, force-interval curves were fitted with an equation which used five parameters to define the shape. At test intervals < 10 sec, force-interval curves were similar in young and aged hearts. At longer intervals, however, force was greater in atria from old animals than in atria from young animals. The parameters E0, which reflects force amplitude at long intervals, was significantly increased in old atria while the parameter gamma, which reflects the time course of force decay at long intervals, was significantly reduced. Thus, at long test intervals the force-interval relation is markedly affected by the aging process.