Norepinephrine stimulates apoptosis in adult rat ventricular myocytes by activation of the β-adrenergic pathway

Background-Myocardial sympathetic activity is increased in heart failure. We tested the hypothesis that norepinephrine (NE) stimulates apoptosis in adult rat ventricular myocytes in vitro. Methods and Results-Myocytes were exposed to NE alone (10 mu mol/L), NE+propranolol (2 mu mol/L), NE+prazosin (0.1 mu mol/L), or isoproterenol (ISO, 10 mu mol/L) for 24 hours. NE and ISO decreased the number of viable myocytes by approximate to 35%. This effect was completely blocked by the beta-adrenergic antagonist propranolol but was not affected by the alpha(1)-adrenergic antagonist prazosin. NE increased DNA laddering on agarose gel electrophoresis and increased the percentage of cells that were stained by terminal deoxynucleotidyl transferase-mediated nick end-labeling from 5.8+/-1.0% to 21.0+/-2.3% (P<0.01; n=4). NE likewise increased the percentage of apoptotic cells with hypodiploid DNA content as assessed by flow cytometry from 7.8+/-0.7% to 16.7+/-2.2% (P<0.01; n=6), and this effect was abolished by propranolol but not prazosin. ISO and forskolin (10 mu mol/L) mimicked the effect of NE, increasing the percentage of apoptotic cells to 14.7+/-1.9% and 14.4+/-2.2%, respectively. NE-stimulated apoptosis was abolished by the protein kinase A inhibitor H-89 (20 mu mol/L) or the voltage-dependent calcium channel blockers diltiazem and nifedipine, Conclusions-NE, acting via the beta-adrenergic pathway, stimulates apoptosis in adult rat cardiac myocytes in vitro. This effect is mediated by protein kinase A and requires calcium entry via voltage-dependent calcium channels. NE-stimulated apoptosis of cardiac myocytes may contribute to the progression of myocardial failure.