title: Effects of increased systolic Ca²⁺ and phospholamban phosphorylation during β-adrenergic stimulation on Ca²⁺ transient kinetics in cardiac myocytes.
abstract: Previous studies demonstrated higher systolic intracellular Ca(2+) concentration ([Ca(2+)](i)) amplitudes result in faster [Ca(2+)](i) decline rates, as does β-adrenergic (β-AR) stimulation. The purpose of this study is to determine the major factor responsible for the faster [Ca(2+)](i) decline rate with β-AR stimulation, the increased systolic Ca(2+) concentration levels, or phosphorylation of phospholamban. Mouse myocytes were perfused under basal conditions [1 mM extracellular Ca(2+) concentration ([Ca(2+)](o))], followed by high extracellular Ca(2+) (3 mM [Ca(2+)](o)), washout with 1 mM [Ca(2+)](o), followed by 1 μM isoproterenol (ISO) with 1 mM [Ca(2+)](o). ISO increased Ser(16) phosphorylation compared with 3 mM [Ca(2+)](o), whereas Thr(17) phosphorylation was similar. Ca(2+) transient (CaT) (fluo 4) data were obtained from matched CaT amplitudes with 3 mM [Ca(2+)](o) and ISO. [Ca(2+)](i) decline was significantly faster with ISO compared with 3 mM [Ca(2+)](o). Interestingly, the faster decline with ISO was only seen during the first 50% of the decline. CaT time to peak was significantly faster with ISO compared with 3 mM [Ca(2+)](o). A Ca(2+)/calmodulin-dependent protein kinase (CAMKII) inhibitor (KN-93) did not affect the CaT decline rates with 3 mM [Ca(2+)](o) or ISO but normalized ISO's time to peak with 3 mM [Ca(2+)](o). Thus, during β-AR stimulation, the major factor for the faster CaT decline is due to Ser(16) phosphorylation, and faster time to peak is due to CAMKII activation.
authors.affiliation: Department of Physiology & Cell Biology, Davis Heart and Lung Research Institute, The Ohio State University, Columbus, Ohio 43210, USA.
authors.forename: Steve R
authors.initials: SR
authors.lastname: Roof
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Shannon
authors.forename: Paul M L
authors.initials: PM
authors.lastname: Janssen
authors.forename: Mark T
authors.initials: MT
authors.lastname: Ziolo
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D058666:Adrenergic beta-2 Receptor Agonists / Q000494:pharmacology; D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000818:Animals; D001596:Benzylamines / Q000494:pharmacology; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects*; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2 / Q000037:antagonists & inhibitors / Q000378:metabolism; D004789:Enzyme Activation / Q000502:physiology; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D007700:Kinetics; D051379:Mice; D008810:Mice, Inbred C57BL; D032383:Myocytes, Cardiac / Q000187:drug effects*; D010766:Phosphorylation; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D012694:Serine / Q000378:metabolism; D013449:Sulfonamides / Q000494:pharmacology; D000099211:Phospholamban; D000096926:Benzenesulfonamides
chemical_list: D000251:Adenosine Triphosphatases; D058666:Adrenergic beta-2 Receptor Agonists; D000318:Adrenergic beta-Agonists; D001596:Benzylamines; D002118:Calcium; D002135:Calcium-Binding Proteins; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D007545:Isoproterenol; D012694:Serine; D013449:Sulfonamides; D000099211:Phospholamban; C072105:KN 93; D000096926:Benzenesulfonamides