Maximal force generation was ~20% lower in muscle fibers from aged rats (P=0.02), but myosin ATPase activity did not differ between aged and young rats (697 vs 686 microM/s; P=0.89).
Absolute Event Rate: 697% vs 686%
p-value: p=0.89
We tested the hypothesis that age-associated decline in muscle function is related to a change in myosin ATPase activity. Single, glycerinated semimembranosus fibers from young (8-12 mo) and aged (32-37 mo) Fischer 344 x Brown Norway male rats were analyzed simultaneously for force and myosin ATPase activity over a range of Ca2+ concentrations. Maximal force generation was ~20% lower in fibers from aged animals (P = 0.02), but myosin ATPase activity was not different between fibers from young and aged rats: 686 +/- 46 (n = 30) and 697 +/- 46 microM/s (n = 33) (P = 0.89). The apparent rate constant for the dissociation of strong-binding myosin from actin was calculated to be ~30% greater in fibers from aged animals (P = 0.03), indicating that the lower force produced by fibers from aged animals is due to a greater flux of myosin heads from the strong-binding state to the weak-binding state during contraction. This is in agreement with our previous electron paramagnetic resonance experiments that showed a reduced fraction of myosin heads in the strong-binding state during a maximal isometric contraction in fibers from older rats.
Lowe et al. (Mon,) conducted a other in Age-associated decline in muscle function (n=63). Advanced age vs. Young age (8-12 months) was evaluated on Myosin ATPase activity (microM/s) (p=0.89). Maximal force generation was ~20% lower in muscle fibers from aged rats (P=0.02), but myosin ATPase activity did not differ between aged and young rats (697 vs 686 microM/s; P=0.89).