title: Phospholemman and beta-adrenergic stimulation in the heart.
abstract: Phosphorylation at serine 68 of phospholemman (PLM) in response to beta-adrenergic stimulation results in simultaneous inhibition of cardiac Na(+)/Ca(2+) exchanger NCX1 and relief of inhibition of Na(+)-K(+)-ATPase. The role of PLM in mediating beta-adrenergic effects on in vivo cardiac function was investigated with congenic PLM-knockout (KO) mice. Echocardiography showed similar ejection fraction between wild-type (WT) and PLM-KO hearts. Cardiac catheterization demonstrated higher baseline contractility (+dP/dt) but similar relaxation (-dP/dt) in PLM-KO mice. In response to isoproterenol (Iso), maximal +dP/dt was similar but maximal -dP/dt was reduced in PLM-KO mice. Dose-response curves to Iso (0.5-25 ng) for WT and PLM-KO hearts were superimposable. Maximal +dP/dt was reached 1-2 min after Iso addition and declined with time in WT but not PLM-KO hearts. In isolated myocytes paced at 2 Hz. contraction and intracellular Ca(2+) concentration ([Ca(2+)](i)) transient amplitudes and [Na(+)](i) reached maximum 2-4 min after Iso addition, followed by decline in WT but not PLM-KO myocytes. Reducing pacing frequency to 0.5 Hz resulted in much smaller increases in [Na(+)](i) and no decline in contraction and [Ca(2+)](i) transient amplitudes with time in Iso-stimulated WT and PLM-KO myocytes. Although baseline Na(+)-K(+)-ATPase current was 41% higher in PLM-KO myocytes because of increased alpha(1)- but not alpha(2)-subunit activity, resting [Na(+)](i) was similar between quiescent WT and PLM-KO myocytes. Iso increased alpha(1)-subunit current (I(alpha1)) by 73% in WT but had no effect in PLM-KO myocytes. Iso did not affect alpha(2)-subunit current (I(alpha2)) in WT and PLM-KO myocytes. In both WT and NCX1-KO hearts, PLM coimmunoprecipitated with Na(+)-K(+)-ATPase alpha(1)- and alpha(2)-subunits, indicating that association of PLM with Na(+)-K(+)-ATPase did not require NCX1. We conclude that under stressful conditions in which [Na(+)](i) was high, beta-adrenergic agonist-mediated phosphorylation of PLM resulted in time-dependent reduction in inotropy due to relief of inhibition of Na(+)-K(+)-ATPase.
authors.affiliation: Department of Medicine, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA.
authors.forename: JuFang
authors.initials: J
authors.lastname: Wang
authors.forename: Erhe
authors.initials: E
authors.lastname: Gao
authors.forename: Jianliang
authors.initials: J
authors.lastname: Song
authors.forename: Xue-Qian
authors.initials: XQ
authors.lastname: Zhang
authors.forename: Jifen
authors.initials: J
authors.lastname: Li
authors.forename: Walter J
authors.initials: WJ
authors.lastname: Koch
authors.forename: Amy L
authors.initials: AL
authors.lastname: Tucker
authors.forename: Kenneth D
authors.initials: KD
authors.lastname: Philipson
authors.forename: Tung O
authors.initials: TO
authors.lastname: Chan
authors.forename: Arthur M
authors.initials: AM
authors.lastname: Feldman
authors.forename: Joseph Y
authors.initials: JY
authors.lastname: Cheung
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D006321:Heart / Q000187:drug effects; D007545:Isoproterenol / Q000494:pharmacology; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D023421:Models, Animal; D009200:Myocardial Contraction / Q000187:drug effects; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D032383:Myocytes, Cardiac / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D011943:Receptors, Adrenergic, beta / Q000378:metabolism*; D019831:Sodium-Calcium Exchanger / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism
chemical_list: D000318:Adrenergic beta-Agonists; D008565:Membrane Proteins; D010750:Phosphoproteins; D011943:Receptors, Adrenergic, beta; D019831:Sodium-Calcium Exchanger; C069141:phospholemman; D000254:Sodium-Potassium-Exchanging ATPase; D007545:Isoproterenol; D002118:Calcium