title: Evidence that the H1-H2 domain of alpha1 subunit of (Na++K+)-ATPase participates in the regulation of cardiac contraction.
abstract: (Na++K+)-ATPase (NKA) plays an important role in ion homeostasis and regulates cardiac contraction. To understand the molecular basis of its cardiac regulatory functions, we investigated whether the primary structure of the H1-H2 domain in alpha-1 (alpha1) subunit of the enzyme plays a role in myocardial contractile regulation. Here we show that site-specific binding to this 1 H1-H2 domain with a targeted antibody (SSA78) markedly augments intracellular Ca2+ transients and contraction of rat ventricular cardiomyocytes without inactivating NKA. In vivo SSA78 infusion in mice results in a positive inotropic effect with enhanced contractile function yet no change in relaxation, indicating a direct cardiac effect linked to the H1-H2 domain. Competitive immunofluorescent staining and flow cytometry reveal that SSA78 binding is antagonized by ouabain, supporting the interaction of SSA78 at one of the glycoside-effecter sites. These new findings suggest that the H1-H2 domain of 1 subunit of NKA is a critical determinant of enzyme biologic activity, which couples to enhanced myocyte calcium transient and inotropic action.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, 108 North Greene St., Room 308, Baltimore, MD 21201, USA. kxu002@umaryland.edu
authors.forename: Kai Y
authors.initials: KY
authors.lastname: Xu
authors.forename: Eiki
authors.initials: E
authors.lastname: Takimoto
authors.forename: George J
authors.initials: GJ
authors.lastname: Juang
authors.forename: Qi
authors.initials: Q
authors.lastname: Zhang
authors.forename: Holly
authors.initials: H
authors.lastname: Rohde
authors.forename: Allen C
authors.initials: AC
authors.lastname: Myers
mesh_terms: D000818:Animals; D000906:Antibodies / Q000378:metabolism / Q000494:pharmacology / Q000502:physiology; D000918:Antibody Specificity / Q000502:physiology; D002118:Calcium / Q000378:metabolism; D002316:Cardiotonic Agents / Q000494:pharmacology; D004285:Dogs; D006321:Heart / Q000187:drug effects; D051379:Mice; D009200:Myocardial Contraction / Q000502:physiology*; D032383:Myocytes, Cardiac / Q000737:chemistry / Q000378:metabolism; D010455:Peptides / Q000138:chemical synthesis / Q000276:immunology / Q000502:physiology*; D017434:Protein Structure, Tertiary / Q000502:physiology; D011817:Rabbits; D051381:Rats; D000254:Sodium-Potassium-Exchanging ATPase / Q000737:chemistry / Q000276:immunology / Q000502:physiology*
chemical_list: D000906:Antibodies; D002316:Cardiotonic Agents; D010455:Peptides; C499075:Atp1a1 protein, rat; D000254:Sodium-Potassium-Exchanging ATPase; D002118:Calcium