Epac-mediated Activation of Phospholipase Cɛ Plays a Critical Role in β-Adrenergic Receptor-dependent Enhancement of Ca2+ Mobilization in Cardiac Myocytes

• DOI: 10.1074/jbc.m608495200
• Publication Date: 2006-12-19T01:12:48Z
• Authors: Emily A. Oestreich; Huan Wang; Sundeep Malik; Katherine A. Kapr...; Burns C. Blaxall; Grant G. Kelley; Robert T. Dirksen; Alan V. Smrcka
• Keywords: Mice, Knockout; 0301 basic medicine; Mice; Sarcoplasmic Reticulum; 03 medical and health sciences; Phosphoinositide Phospholipase C; rap GTP-Binding Proteins; Transduction, Genetic; Type C Phospholipases; Receptors, Adrenergic, beta; Cyclic AMP; Animals; Guanine Nucleotide Exchange Factors; Calcium; Myocytes, Cardiac; Calcium Signaling; Evoked Potentials; Cells, Cultured

Recently we demonstrated that PLC(epsilon) plays an important role in beta-adrenergic receptor (betaAR) stimulation of Ca(2+)-induced Ca(2+) release (CICR) in cardiac myocytes. Here we have reported for the first time that a pathway downstream of betaAR involving the cAMP-dependent Rap GTP exchange factor, Epac, and PLC(epsilon) regulates CICR in cardiac myocytes. To demonstrate a role for Epac in the stimulation of CICR, cardiac myocytes were treated with an Epac-selective cAMP analog, 8-4-(chlorophenylthio)-2'-O-methyladenosine-3',5'-monophosphate (cpTOME). cpTOME treatment increased the amplitude of electrically evoked Ca(2+) transients, implicating Epac for the first time in cardiac CICR. This response is abolished in PLC(epsilon)(-/-) cardiac myocytes but rescued by transduction with PLC(epsilon), indicating that Epac is upstream of PLC(epsilon). Furthermore, transduction of PLC(epsilon)(+/+) cardiac myocytes with a Rap inhibitor, RapGAP1, significantly inhibited isoproterenol-dependent CICR. Using a combination of cpTOME and PKA-selective activators and inhibitors, we have shown that betaAR-dependent increases in CICR consist of two independent components mediated by PKA and the novel Epac/(epsilon) pathway. We also show that Epac/PLC(epsilon)-dependent effects on CICR are independent of sarcoplasmic reticulum loading and Ca(2+) clearance mechanisms. These data define a novel endogenous PKA-independent betaAR-signaling pathway through cAMP-dependent Epac activation, Rap, and PLC(epsilon) that enhances intracellular Ca(2+) release in cardiac myocytes.