AJP - Heart and Circulatory Physiology, Vol 246, Issue 6 784-H791, Copyright © 1984 by American Physiological Society

ARTICLES

Excitation-contraction in rat myocardium: alterations with adult aging

J. Y. Wei, H. A. Spurgeon and E. G. Lakatta

Simultaneous transmembrane action potential (TAP) and isometric contraction measurements were made in thin right ventricular papillary muscles isolated from senescent (S, 24-26 mo) and young adult (YA, 6-8 mo) rat hearts. At the peak of the length-tension curve in the steady state at 24 min-1 at 29 degrees C in perfusate [Ca2+] [( Ca2+]e) of 0.375 or 2.5 mM, contractile tension developed in response to excitation (DT) and the maximum rate of tension development (dT/dt) were not age-related; contraction duration (CD) was 17 and 27% greater in S than YA in the low and high [Ca2+]e, respectively (P less than 0.001); resting membrane potential was not age related. TAP time above zero mV, integrated area above zero mV, and times to 75% (T75) and 90% (T90) repolarization were approximately twofold greater in S than in YA in both [Ca2+]e (P less than 0.001). Changes in steady-state T75 and T90 due to an increase in [Ca2+]e from 0.375 to 2.5 mM were significantly correlated with those in CD, DT, and dT/dt in S but not in YA. We conclude that in the senescent myocardium a prolonged and greater extent of depolarization is related to the prolonged CD and may also be a determinant of the peak force developed in response to excitation under some conditions.

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