Inhibition of protein phosphatase 1 induces apoptosis in neonatal rat cardiac myocytes: role of adrenergic receptor stimulation

The mechanisms that regulate cardiac myocyte apoptosis are not well underst ood. To study the role of protein phosphatase 1 (PP1) and 2A (PP2A) in apop tosis, we exposed cultured neonatal rat cardiac myocytes to the phosphatase inhibitor okadaic acid (OA). Exposure (18 h) to 100 nM OA (a concentration which inhibits both PP1 and PP2A) decreased the number of adherent cells, caused genomic DNA fragmentation, and increased the percentage of apoptotic cells. These effects did not occur at a lower concentration of OA (1 nM) w hich is relatively specific for PP2A. Stimulation of alpha (1)- or beta -ad renergic receptors with norepinephrine (NE) in the presence of propranolol or prazosin partially blocked OA-induced apoptosis as measured by flow cyto metry. Likewise, stimulation of adenylyl cyclase with forskolin reduced OA- induced apoptosis. Conversely, inhibition of protein kinase A with H89 or p rotein kinase C with chelerethrine potentiated OA-induced apoptosis. OA inc reased caspase-3 activity, and this effect was reduced by NE. Thus, inhibit ion of PP1 stimulates apoptosis in NRVM and stimulation of adrenergic recep tors protects against OA-induced apoptosis.