title: Sodium-calcium exchanger (NCX-1) and calcium modulation: NCX protein expression patterns and regulation of early heart development.
abstract: Ouabain-induced inhibition of early heart development indicated that Na/K-ATPase plays an important role in maintaining normal ionic balances during differentiation of cardiomyocytes (Linask and Gui [1995] Dev Dyn 203:93-105). Inhibition of the sodium pump is generally accepted to affect the activity of the Na(+)-Ca(++) exchanger (NCX) to increase intracellular [Ca(++)]. These previous findings suggested that Ca(++) signaling may be an important modulator during differentiation of cardiomyocytes. In order to identify a connection between heart development and NCX-mediated Ca(++) regulation, we determined the embryonic spatiotemporal protein expression pattern of NCX-1 during early developmental stages. In both chick and mouse embryos, NCX-1 (the cardiac NCX isoform) is asymmetrically expressed during gastrulation; in the right side of the Hensen's node in the chick, in the right lateral mesoderm in the mouse. At slightly later stages, NCX-1 is expressed in the heart fields at comparable stages of heart development, in the chick at stage 7 and in the mouse at embryonic day (ED) 7.5. By ED 8 in the mouse, the exchanger protein displays a rostrocaudal difference in cardiac expression and an outer curvature-inner curvature ventricular difference. By ED 9.5, cardiac expression has increased from that seen at ED8 and NCX-1 is distributed throughout the myocardium consistent with the possibility that it is important in regulating initial cardiac contractile function. Only a low level of expression is detected in inflow and outflow regions. To substantiate a role for the involvement of calcium-mediated signaling, using pharmacologic approaches, ionomycin (a Ca(++) ionophore) was shown to perturb cardiac cell differentiation in a manner similar to ouabain as assayed by cNkx2.5 and sarcomeric myosin heavy chain expression. In addition, we show that an inhibitor of NCX, KB-R7943, can similarly and adversely affect early cardiac development at stage 4/5 and arrests cardiac cell contractility in 12-somite embryos. Thus, based upon NCX-1 protein expression patterns in the embryo, experimental Ca(++) modulation, and inhibition of NCX activity by KB-R7943, these results suggest an early and central role for calcium-mediated signaling in cardiac cell differentiation and NCX's regulation of the initial heartbeats in the embryo.
authors.affiliation: Department of Cell Biology, University of Medicine and Dentistry of New Jersey (UMDNJ), School of Osteopathic Medicine, Stratford, New Jersey 08084, USA. linaskkk@umdnj.edu
authors.forename: K K
authors.initials: KK
authors.lastname: Linask
authors.forename: M D
authors.initials: MD
authors.lastname: Han
authors.forename: M
authors.initials: M
authors.lastname: Artman
authors.forename: C A
authors.initials: CA
authors.lastname: Ludwig
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002642:Chick Embryo; D005314:Embryonic and Fetal Development; D004791:Enzyme Inhibitors / Q000494:pharmacology; D020869:Gene Expression Profiling; D006321:Heart / Q000187:drug effects / Q000196:embryology* / Q000502:physiology; D015759:Ionomycin / Q000494:pharmacology; D007476:Ionophores / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D009200:Myocardial Contraction; D009206:Myocardium / Q000378:metabolism; D010042:Ouabain / Q000494:pharmacology; D012333:RNA, Messenger; D019831:Sodium-Calcium Exchanger / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D013890:Thiourea / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: C101670:2-(2-(4-(4-nitrobenzyloxy)phenyl)ethyl)isothiourea methanesulfonate; D004791:Enzyme Inhibitors; D007476:Ionophores; D012333:RNA, Messenger; D019831:Sodium-Calcium Exchanger; C110374:sodium-calcium exchanger 1; D015759:Ionomycin; D010042:Ouabain; D013890:Thiourea; D002118:Calcium