title: Low-dose ouabain administration increases Na⁺,K⁺-ATPase activity and reduces cardiac force development in rats.
abstract: BACKGROUND
  Ouabain is a digitalis compound that inhibits the Na(+),K(+)-ATPase (NKA) activity inducing increment in cardiac force. However, this effect seems to be dose dependent. At low concentration, ouabain can induce an increase of NKA activity.
  
  
  METHODS
  We investigated the effects of ouabain administration (25 μg/kg/day) for 15 days on cardiac contractility and NKA activity. Blood pressure and left ventricular papillary muscle contraction from placebo and ouabain-treated rats for 15 (OUA15) days were evaluated. Isometric force, post-rest potentiation, positive inotropic intervention produced by isoproterenol, and tetanic tension were measured. The activity and protein expression levels of α1 and α2 isoforms of NKA, sodium calcium exchanger (NCX), sarcoplasmic reticulum calcium ATPase (SERCA2a) and phospholamban (PLB) were also measured.
  
  
  RESULTS
  Systolic and diastolic blood pressures increased after treatment with ouabain. However, isometric tension was reduced in the ouabain treated group. Post-rest potentiation, time parameters, inotropic interventions by isoproterenol and tetanic tension did not change. In the ouabain treated group, NKA activity was increased (Oua 406.16 ± 70.6 vs. CT 282.80 ± 80.5) while protein expression of the α1 isoform of NKA was reduced (Oua 0.97 ± 0.06 vs. CT 0.76 ± 0.05). No changes were observed in protein expression of α2 isoform of NKA, NCX, SERCA2a and PLB. Therefore, although 15-day ouabain treatment increases blood pressure (Oua: 116.4 ± 3 vs. CT: 99.9 ± 3), treatment also reduces isometric tension development (Oua: 0.34 ± 0.14 vs. CT: 0.56 ± 0.22).
  
  
  CONCLUSIONS
  We suggest that the effects induced by ouabain in the isolated cardiac muscle could be related at least in part, to changes in NKA activity.
authors.affiliation: Centro de Ciências Agrárias, Universidade Federal do Espirito Santo, Alegre, ES, Brazil. Electronic address: eduardofrizzerameira@gmail.com.
authors.forename: Eduardo F
authors.initials: EF
authors.lastname: Meira
authors.affiliation: Centro de Ciências Agrárias, Universidade Federal do Espirito Santo, Alegre, ES, Brazil.
authors.forename: Fabiana Dayse M
authors.initials: FD
authors.lastname: Siman
authors.affiliation: Centro de Ciências da Saúde, Universidade Federal do Espírito Santo, Vitória, ES, Brazil.
authors.forename: Thais de O
authors.initials: Tde O
authors.lastname: Faria
authors.affiliation: Centro de Ciências da Saúde, Universidade Federal do Espírito Santo, Vitória, ES, Brazil.
authors.forename: Rogerio F Ribeiro
authors.initials: RF
authors.lastname: Júnior
authors.affiliation: Centro de Ciências da Saúde, Universidade Federal do Espírito Santo, Vitória, ES, Brazil.
authors.forename: Priscila R
authors.initials: PR
authors.lastname: de Batista
authors.affiliation: Centro de Ciências da Saúde, Universidade Federal do Espírito Santo, Vitória, ES, Brazil.
authors.forename: Ivanita
authors.initials: I
authors.lastname: Stefanon
authors.affiliation: Escola de Ensino Superior da Santa Casa de Misericórdia de Vitória, EMESCAM, Vitória, ES, Brazil.
authors.forename: Dalton V
authors.initials: DV
authors.lastname: Vassallo
authors.affiliation: Centro de Ciências da Saúde, Universidade Federal do Espírito Santo, Vitória, ES, Brazil.
authors.forename: Alessandra S
authors.initials: AS
authors.lastname: Padilha
mesh_terms: D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D002135:Calcium-Binding Proteins / Q000378:metabolism; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects* / Q000502:physiology; D009206:Myocardium / Q000378:metabolism; D010042:Ouabain / Q000008:administration & dosage* / Q000494:pharmacology*; D010210:Papillary Muscles / Q000187:drug effects / Q000502:physiology; D051381:Rats; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000378:metabolism; D019831:Sodium-Calcium Exchanger / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D013268:Stimulation, Chemical; D000099211:Phospholamban
chemical_list: D002135:Calcium-Binding Proteins; D007545:Isoproterenol; D010042:Ouabain; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D019831:Sodium-Calcium Exchanger; D000254:Sodium-Potassium-Exchanging ATPase; D000099211:Phospholamban
keywords: Hypertension; Na(+),K(+)-ATPase activity; Ouabain; Papillary muscles