title: Epac-mediated activation of phospholipase C(epsilon) plays a critical role in beta-adrenergic receptor-dependent enhancement of Ca2+ mobilization in cardiac myocytes.
abstract: 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.
authors.affiliation: Department of Pharmacology, University of Rochester School of Medicine, Rochester, New York 14642, USA.
authors.forename: Emily A
authors.initials: EA
authors.lastname: Oestreich
authors.forename: Huan
authors.initials: H
authors.lastname: Wang
authors.forename: Sundeep
authors.initials: S
authors.lastname: Malik
authors.forename: Katherine A
authors.initials: KA
authors.lastname: Kaproth-Joslin
authors.forename: Burns C
authors.initials: BC
authors.lastname: Blaxall
authors.forename: Grant G
authors.initials: GG
authors.lastname: Kelley
authors.forename: Robert T
authors.initials: RT
authors.lastname: Dirksen
authors.forename: Alan V
authors.initials: AV
authors.lastname: Smrcka
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D005071:Evoked Potentials / Q000187:drug effects / Q000502:physiology; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D032383:Myocytes, Cardiac / Q000166:cytology / Q000201:enzymology*; D054801:Phosphoinositide Phospholipase C; D011943:Receptors, Adrenergic, beta / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000201:enzymology / Q000235:genetics; D014161:Transduction, Genetic; D010738:Type C Phospholipases / Q000172:deficiency / Q000378:metabolism*; D020668:rap GTP-Binding Proteins / Q000378:metabolism
chemical_list: C482601:Epac protein, mouse; D020662:Guanine Nucleotide Exchange Factors; D011943:Receptors, Adrenergic, beta; D000242:Cyclic AMP; D010738:Type C Phospholipases; D054801:Phosphoinositide Phospholipase C; C423320:phospholipase C epsilon; D020668:rap GTP-Binding Proteins; D002118:Calcium