title: Regulation of Ca2+ signaling in transgenic mouse cardiac myocytes overexpressing calsequestrin.
abstract: To probe the physiological role of calsequestrin in excitation-contraction coupling, transgenic mice overexpressing cardiac calsequestrin were developed. Transgenic mice exhibited 10-fold higher levels of calsequestrin in myocardium and survived into adulthood, but had severe cardiac hypertrophy, with a twofold increase in heart mass and cell size. In whole cell-clamped transgenic myocytes, Ca2+ channel- gated Ca2+ release from the sarcoplasmic reticulum was strongly suppressed, the frequency of occurrence of spontaneous or Ca2+ current-triggered "Ca2+ sparks" was reduced, and the spark perimeter was less defined. In sharp contrast, caffeine-induced Ca2+ transients and the resultant Na+-Ca2+ exchanger currents were increased 10-fold in transgenic myocytes, directly implicating calsequestrin as the source of the contractile-dependent pool of Ca2+. Interestingly, the proteins involved in the Ca2+-release cascade (ryanodine receptor, junctin, and triadin) were downregulated, whereas Ca2+-uptake proteins (Ca2+-ATPase and phospholamban) were unchanged or slightly increased. The parallel increase in the pool of releasable Ca2+ with overexpression of calsequestrin and subsequent impairment of physiological Ca2+ release mechanism show for the first time that calsequestrin is both a storage and a regulatory protein in the cardiac muscle Ca2+-signaling cascade. Cardiac hypertrophy in these mice may provide a novel model to investigate the molecular determinants of heart failure.
authors.affiliation: Krannert Institute of Cardiology, Indiana University School of Medicine, Indianapolis, Indiana 46202, USA.
authors.forename: L R
authors.initials: LR
authors.lastname: Jones
authors.forename: Y J
authors.initials: YJ
authors.lastname: Suzuki
authors.forename: W
authors.initials: W
authors.lastname: Wang
authors.forename: Y M
authors.initials: YM
authors.lastname: Kobayashi
authors.forename: V
authors.initials: V
authors.lastname: Ramesh
authors.forename: C
authors.initials: C
authors.lastname: Franzini-Armstrong
authors.forename: L
authors.initials: L
authors.lastname: Cleemann
authors.forename: M
authors.initials: M
authors.lastname: Morad
mesh_terms: D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000502:physiology*; D015220:Calcium Channels / Q000502:physiology; D002135:Calcium-Binding Proteins; D002155:Calsequestrin / Q000502:physiology*; D006332:Cardiomegaly / Q000235:genetics; D002352:Carrier Proteins / Q000378:metabolism; D002451:Cell Compartmentation / Q000187:drug effects; D005786:Gene Expression Regulation; D007425:Intracellular Membranes / Q000648:ultrastructure; D047908:Intracellular Signaling Peptides and Proteins; D015640:Ion Channel Gating; D008565:Membrane Proteins; D051379:Mice; D008822:Mice, Transgenic; D018613:Microscopy, Confocal; D008854:Microscopy, Electron; D006899:Mixed Function Oxygenases; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism; D009200:Myocardial Contraction; D009206:Myocardium / Q000378:metabolism* / Q000648:ultrastructure; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D015398:Signal Transduction; D019831:Sodium-Calcium Exchanger / Q000378:metabolism
chemical_list: D015220:Calcium Channels; D002135:Calcium-Binding Proteins; D002155:Calsequestrin; D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D009124:Muscle Proteins; D019837:Ryanodine Receptor Calcium Release Channel; D019831:Sodium-Calcium Exchanger; C498269:TRDN protein, human; C498270:Trdn protein, mouse; C070048:triadin; D002110:Caffeine; C498841:Asph protein, mouse; D006899:Mixed Function Oxygenases; D002118:Calcium