THE FORCE-INTERVAL RELATION IN AGED HAMSTER HEART

This study determined whether aging affects the force-interval relatio n 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 int erposing test intervals (0.3-600 sec) on the force of a test beat foll owing the interval (force-interval relation) were examined. To quantif y differences, force-interval curves were fitted with an equation whic h used five parameters to define the shape. At test intervals < 10 sec , force-interval curves were similar in young and aged hearts. At long er intervals, however, force was greater in atria from old animals tha n in atria from young animals. The parameter E(0), which reflects forc e amplitude at long intervals, was significantly increased in old atri a while the parameter gamma, which reflects the time course of force d ecay at long intervals, was significantly reduced. Thus, at long test intervals the force-interval relation is markedly affected by the agin g process.