Calcium sensitivity of myocardial actomyosin ATPase in young and mature male Fischer rats. A brief note.

Although myocardial actomyosin ATPase specific activity determined at Ca2+ levels of 1 x 10(-3) to 1 x 10(-2) M is consistently higher in two-month old male Fischer rats than in twelve-month old individuals, this difference can be eliminated if the enzyme is assayed at lower calcium concentrations. This suggests that the previously reported, declining actomyosin ATPase activity in the rat myocardium with advancing age may represent an age-related diminished ability of calcium to reverse the known inhibition upon actomyosin ATPase by the regulatory proteins.