The “Heartbreak” of Older Age

Differences in various aspects of excitation-contraction coupling mechanisms measured between adult (6–9 months) and senescent (24–26 months) rat hearts. A. Transmembrane action potential, and (B) isometric contraction [from (6) ]. C. Cytosolic calcium transient, measured by a change in the luminescence of aequorin injected into several cells comprising the muscle preparation [from (7) ]. D. Sarcoplasmic reticulum Ca²⁺ uptake rate [from (8) ].