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Department of Physiology, University of Wisconsin School of Medicine, Madison, Wisconsin 53706
Normal aging of
the rodent heart results in prominent prolongation of the twitch. We
tested the hypothesis that increased expression of
-myosin heavy
chain (MHC), as occurs in the normal aging process in the rodent heart,
contributes to the prolongation of the twitch by depressing the
kinetics of cross-bridge interaction. Using 3-, 9-, 21-, and 33-mo-old
male Fischer 344 × Brown Norway F1
hybrid rats, we examined both the rate of tension development (kCa) and
unloaded shortening velocity in chemically skinned myocardium. Although
kCa in all four
age groups was dependent on the level of
Ca2+ activation, both submaximal
and maximal kCa
were significantly slower in 9-, 21-, and 33-mo-old rats relative to
3-mo-old rats. Furthermore, unloaded shortening velocity was
significantly reduced in 9-, 21-, and 33-mo-old rats compared with
3-mo-old rats. Collectively, these data strongly suggest that the
aging-related increase in
-MHC expression results in a progressive
slowing of cross-bridge interaction kinetics in skinned myocardium,
which most likely contributes to the overall aging-dependent reduction
in myocardial functional capacity.
myosin heavy chain; caged calcium; cross-bridge kinetics; Fischer 344 × Brown Norway rats
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