title: Effects of clenbuterol on contractility and Ca2+ homeostasis of isolated rat ventricular myocytes.
abstract: Clenbuterol, a compound classified as a beta2-adrenoceptor (AR) agonist, has been employed in combination with left ventricular assist devices (LVADs) to treat patients with severe heart failure. Previous studies have shown that chronic administration of clenbuterol affects cardiac excitation-contraction coupling. However, the acute effects of clenbuterol and the signaling pathway involved remain undefined. We investigated the acute effects of clenbuterol on isolated ventricular myocyte sarcomere shortening, Ca2+ transients, and L-type Ca2+ current and compared these effects to two other clinically used beta2-AR agonists: fenoterol and salbutamol. Clenbuterol (30 microM) produced a negative inotropic response, whereas fenoterol showed a positive inotropic response. Salbutamol had no significant effects. Clenbuterol reduced Ca2+ transient amplitude and L-type Ca2+ current. Selective beta1-AR blockade did not affect the action of clenbuterol on sarcomere shortening but significantly reduced contractility in the presence of fenoterol and salbutamol (P < 0.05). Incubation with 2 microg/ml pertussis toxin significantly reduced the negative inotropic effects of 30 microM clenbuterol. In addition, overexpression of inhibitory G protein (Gi) by adenoviral transfection induced a stronger clenbuterol-mediated negative inotropic effect, suggesting the involvement of the Gi protein. We conclude that clenbuterol does not increase and, at high concentrations, significantly depresses contractility of isolated ventricular myocytes, an effect not seen with fenoterol or salbutamol. In its negative inotropism, clenbuterol predominantly acts through Gi, and the consequent downstream signaling pathways activation may explain the beneficial effects observed during chronic administration of clenbuterol in patients treated with LVADs.
authors.affiliation: Heart Science Centre, National Heart & Lung Institute, Imperial College, London, United Kingdom.
authors.forename: U
authors.initials: U
authors.lastname: Siedlecka
authors.forename: M
authors.initials: M
authors.lastname: Arora
authors.forename: T
authors.initials: T
authors.lastname: Kolettis
authors.forename: G K R
authors.initials: GK
authors.lastname: Soppa
authors.forename: J
authors.initials: J
authors.lastname: Lee
authors.forename: M A
authors.initials: MA
authors.lastname: Stagg
authors.forename: S E
authors.initials: SE
authors.lastname: Harding
authors.forename: M H
authors.initials: MH
authors.lastname: Yacoub
authors.forename: C M N
authors.initials: CM
authors.lastname: Terracciano
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000420:Albuterol / Q000494:pharmacology; D000818:Animals; D020746:Calcium Channels, L-Type / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects*; D002478:Cells, Cultured; D002976:Clenbuterol / Q000494:pharmacology*; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D005280:Fenoterol / Q000494:pharmacology; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000235:genetics / Q000378:metabolism; D006333:Heart Failure / Q000188:drug therapy* / Q000378:metabolism / Q000503:physiopathology; D006352:Heart Ventricles / Q000187:drug effects / Q000378:metabolism; D006706:Homeostasis; D018727:Muscarinic Antagonists / Q000494:pharmacology; D009200:Myocardial Contraction / Q000187:drug effects*; D032383:Myocytes, Cardiac / Q000187:drug effects* / Q000378:metabolism; D051381:Rats; D012518:Sarcomeres / Q000187:drug effects / Q000378:metabolism; D014162:Transfection
chemical_list: D000318:Adrenergic beta-Agonists; D000319:Adrenergic beta-Antagonists; D020746:Calcium Channels, L-Type; D018727:Muscarinic Antagonists; D005280:Fenoterol; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D000420:Albuterol; D002976:Clenbuterol
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