AJP - Heart and Circulatory Physiology, Vol 242, Issue 3 359-H364, Copyright © 1982 by American Physiological Society
Alterations in mechanical properties of rat papillary muscle during maturation
J. M. Capasso, R. M. Remily and E. H. Sonnenblick
Myocardial performance was measured during maturation using isolated left
ventricular papillary muscles from female Wistar rats. Muscles were studied
isometrically and isotonically, stimulated at 0.1 Hz, perfused with Tyrode
solution having an external calcium concentration of 2.4 mM, and maintained
at 30 degrees C. Heart and body weight increased rapidly during the first 6
mo and then stabilized. Peak isometric developed tension, time to peak
isometric developed tension, and time to half relaxation increased
substantially during the 1- to 10-mo period with little change in the peak
rate of isometric tension rise and peak rate of isometric tension fall. No
difference in resting tension was noted among any groups. Force-velocity
curves from muscles from 2-, 6-, and 10-mo-old animals show a significant
age-related decrease in the isotonic velocity of shortening by as much as
21% between 2 and 10 mo of age. Thus maturation profoundly affects the
contractile state of cardiac muscle, with force of contraction increasing
and velocity of shortening decreasing as a function of age in the rat.
