title: Loss of beta-adrenoceptor response in myocytes overexpressing the Na+/Ca(2+)-exchanger.
abstract: Increased Na+/Ca(2+)-exchanger (NCX) and altered beta-adrenoceptor (betaAR) responses are observed in failing human heart. To determine the possible interaction between these changes, we investigated the effect of NCX overexpression on responses to isoproterenol in adult rat ventricular myocytes. Responses to isoproterenol were largely mediated through the beta1AR in control myocytes. Adenovirally-mediated overexpression of NCX, at levels, which did not alter basal contraction of myocytes, markedly depressed the isoproterenol concentration-response curve. Responses to isoproterenol could be restored to normal by beta2AR blockade, suggesting a beta2AR-mediated inhibition of beta1AR signalling. Pertussis toxin normalised isoproterenol responses in NCX cells, indicating that beta2AR effects were mediated by Gi. Negative-inotropic effects of high concentrations of ICI 118,551, previously shown to be due to beta2AR-Gi coupling, were increased in NCX cells. We conclude that NCX upregulation can markedly alter the consequences of betaAR stimulation and that this may contribute to the alterations in betaAR response seen in failing human heart.
authors.affiliation: Department of Cardiac Medicine, NHLI, Faculty of Medicine, Imperial College London, Dovehouse Street, London SW3 6LY, UK.
authors.forename: Motoki
authors.initials: M
authors.lastname: Sato
authors.forename: Haibin
authors.initials: H
authors.lastname: Gong
authors.forename: Cesare M N
authors.initials: CM
authors.lastname: Terracciano
authors.forename: Hardeep
authors.initials: H
authors.lastname: Ranu
authors.forename: Sian E
authors.initials: SE
authors.lastname: Harding
mesh_terms: D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000818:Animals; D004305:Dose-Response Relationship, Drug; D007545:Isoproterenol / Q000494:pharmacology; D032342:Muscle Cells / Q000187:drug effects / Q000502:physiology*; D009200:Myocardial Contraction / Q000187:drug effects / Q000502:physiology; D037342:Pertussis Toxin / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D018342:Receptors, Adrenergic, beta-1 / Q000378:metabolism*; D018343:Receptors, Adrenergic, beta-2 / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D019831:Sodium-Calcium Exchanger / Q000235:genetics / Q000378:metabolism*; D016276:Ventricular Function
chemical_list: D000319:Adrenergic beta-Antagonists; D018342:Receptors, Adrenergic, beta-1; D018343:Receptors, Adrenergic, beta-2; D011993:Recombinant Fusion Proteins; D019831:Sodium-Calcium Exchanger; D037342:Pertussis Toxin; D007545:Isoproterenol