title: Cholesterol regulates contractility and inotropic response to β2-adrenoceptor agonist in the mouse atria: Involvement of Gi-protein-Akt-NO-pathway.
abstract: Majority of cardiac β2-adrenoceptors is located in cholesterol-rich microdomains. Here, we have investigated the underlying mechanisms by which a slight to moderate cholesterol depletion with methyl-β-cyclodextrin (MβCD, 1 and 5mM) interferes with contractility and inotropic effect of β2-adrenergic agonist (fenoterol, 50μM) in the mouse atria. Treatment with MβCD itself increased amplitude of Ca2+transient but did not change the contraction amplitude due to a clamping action of elevated NO. Cholesterol depletion significantly attenuated the positive inotropic response to fenoterol which is accompanied by increase in NO generation and decrease in Ca2+transient. Influence of 1mM MβCD on the fenoterol-driven changes in both contractility and NO level was strongly attenuated by inhibition of Gi-protein (pertussis toxin), Akt (Akt 1/2 kinase inhibitor) or NO-synthase (L-NAME). After exposure to 5mM MβCD, pertussis toxin or Akt inhibitor could recover the β2-agonist effects on contractility, NO production and Ca2+transient, while L-NAME only reduced NO level. An adenylyl cyclase activator (forskolin, 50nM) had no influence on the MβCD-induced changes in the β2-agonist effects. Obtained results suggest that slight cholesterol depletion upregulates Gi-protein/Akt/NO-synthase signaling that attenuates the positive inotropic response to β2-adrenergic stimulation without altering the Ca2+transient. Whilst moderate cholesterol depletion additionally could suppress the enhancement of the Ca2+transient amplitude caused by the β2-adrenergic agonist administration in Gi-protein/Akt-dependent but NO-independent manner.
authors.affiliation: Department of Normal Physiology, Kazan State Medical University, Kazan 420012, Russia.
authors.forename: Yulia G
authors.initials: YG
authors.lastname: Odnoshivkina
authors.affiliation: Department of Normal Physiology, Kazan State Medical University, Kazan 420012, Russia.
authors.forename: Vaycheslav I
authors.initials: VI
authors.lastname: Sytchev
authors.affiliation: Department of Normal Physiology, Kazan State Medical University, Kazan 420012, Russia. Electronic address: fysio@rambler.ru.
authors.forename: Alexey M
authors.initials: AM
authors.lastname: Petrov
mesh_terms: D058672:Adrenergic beta-2 Receptor Antagonists / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002316:Cardiotonic Agents / Q000494:pharmacology; D002784:Cholesterol / Q000378:metabolism*; D005280:Fenoterol / Q000008:administration & dosage; D006325:Heart Atria / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D009200:Myocardial Contraction / Q000187:drug effects / Q000235:genetics*; D009569:Nitric Oxide / Q000235:genetics / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000235:genetics* / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D047392:beta-Cyclodextrins / Q000494:pharmacology
chemical_list: D058672:Adrenergic beta-2 Receptor Antagonists; D002316:Cardiotonic Agents; D047392:beta-Cyclodextrins; C108732:methyl-beta-cyclodextrin; D005280:Fenoterol; D009569:Nitric Oxide; D002784:Cholesterol; D019001:Nitric Oxide Synthase; D002118:Calcium
keywords: Akt; Atria; Ca(2+); Cholesterol; Contractility; Fenoterol; G(i)-protein; Nitric oxide; Signaling; β2-Adrenoceptor