The “Heartbreak” of Older Age

The efficacy of β adrenergic receptor stimulation withers with advancing age. A. The effect of norepinephrine on the maximum rate of isometric tension development in isolated trabeculae from hearts of varying age. From (21). B. Velocity of cell shortening, and C. the maximum rate of increases of the Indo-1 fluorescence transient, an index of sarcoplasmic reticulum Ca²⁺ release into the cytosol, during the electrically stimulated twitch in single cardiac myocytes isolated from the hearts of rats of varying ages and loaded with the fluorescent probe, Indo-1. From (18). D. Norepinephrine increases the L-type sarcolemmal channel current (I_Ca ). across a range of activating steps to different membrane potentials in single vascular cells potential decline with aging, the norepinephine concentration was 1 x 10^-7 M. From (18) . E. Treatment with norepinephrine (NE) increases phosphorylation of troponin I (TNI) in suspensions of heart cells isolated from hearts of rats of varying age. From (20).