title: A full range of mouse sinoatrial node AP firing rates requires protein kinase A-dependent calcium signaling.
abstract: Recent perspectives on sinoatrial nodal cell (SANC)(*) function indicate that spontaneous sarcoplasmic reticulum (SR) Ca(2+) cycling, i.e. an intracellular "Ca(2+) clock," driven by cAMP-mediated, PKA-dependent phosphorylation, interacts with an ensemble of surface membrane electrogenic molecules ("surface membrane clock") to drive SANC normal automaticity. The role of AC-cAMP-PKA-Ca(2+) signaling cascade in mouse, the species most often utilized for genetic manipulations, however, has not been systematically tested. Here we show that Ca(2+) cycling proteins (e.g. RyR2, NCX1, and SERCA2) are abundantly expressed in mouse SAN and that spontaneous, rhythmic SR generated local Ca(2+) releases (LCRs) occur in skinned mouse SANC, clamped at constant physiologic [Ca(2+)]. Mouse SANC also exhibits a high basal level of phospholamban (PLB) phosphorylation at the PKA-dependent site, Serine16. Inhibition of intrinsic PKA activity or inhibition of PDE in SANC, respectively: reduces or increases PLB phosphorylation, and markedly prolongs or reduces the LCR period; and markedly reduces or accelerates SAN spontaneous firing rate. Additionally, the increase in AP firing rate by PKA-dependent phosphorylation by β-adrenergic receptor (β-AR) stimulation requires normal intracellular Ca(2+) cycling, because the β-AR chronotropic effect is markedly blunted when SR Ca(2+) cycling is disrupted. Thus, AC-cAMP-PKA-Ca(2+) signaling cascade is a major mechanism of normal automaticity in mouse SANC.
authors.affiliation: Laboratory of Cardiovascular Science, Intramural Research Program, Gerontology Research Center, National Institute on Aging, National Institutes of Health, Baltimore MD 21224, USA.
authors.forename: Jie
authors.initials: J
authors.lastname: Liu
authors.forename: Syevda
authors.initials: S
authors.lastname: Sirenko
authors.forename: Magdalena
authors.initials: M
authors.lastname: Juhaszova
authors.forename: Bruce
authors.initials: B
authors.lastname: Ziman
authors.forename: Veena
authors.initials: V
authors.lastname: Shetty
authors.forename: Silvia
authors.initials: S
authors.lastname: Rain
authors.forename: Shweta
authors.initials: S
authors.lastname: Shukla
authors.forename: Harold A
authors.initials: HA
authors.lastname: Spurgeon
authors.forename: Tatiana M
authors.initials: TM
authors.lastname: Vinogradova
authors.forename: Victor A
authors.initials: VA
authors.lastname: Maltsev
authors.forename: Edward G
authors.initials: EG
authors.lastname: Lakatta
mesh_terms: D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology*; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D010507:Periodicity; D010766:Phosphorylation / Q000187:drug effects / Q000502:physiology; D011943:Receptors, Adrenergic, beta / Q000235:genetics / Q000378:metabolism; D019837:Ryanodine Receptor Calcium Release Channel / Q000235:genetics / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000235:genetics / Q000378:metabolism; D012849:Sinoatrial Node / Q000166:cytology / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D019831:Sodium-Calcium Exchanger / Q000235:genetics / Q000378:metabolism; D000099211:Phospholamban
chemical_list: D002118:Calcium; D002135:Calcium-Binding Proteins; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D011943:Receptors, Adrenergic, beta; D019837:Ryanodine Receptor Calcium Release Channel; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D019831:Sodium-Calcium Exchanger; D000099211:Phospholamban; C499849:NCX1 protein, mouse; C506947:Atp2a2 protein, mouse