Age-associated differences in guinea pig myocardial Na+, K+-ATPase activity and ouabain inhibition and in Mg2+-ATPase activity.

The influence of age on activity of cardiac Mg2+-ATPase and Na+, K+-ATPase from guinea pigs was studied. Tissue homogenates and NaI-washed membranes were prepared from the heart tissue of 10- to 12-day-old or greater than 12-month-old male guinea pigs. Tissue homogenates from the young animals had significantly greater enzyme activities than those from the older. Na+, K+-ATPase activity in young tissue preparations was less inhibited by ouabain than in older tissue preparations. These differences may be related to the observations that young animals and humans are less sensitive to cardiac glycosides than adults.