title: Beta3-adrenoceptor in the eel (Anguilla anguilla) heart: negative inotropy and NO-cGMP-dependent mechanism.
abstract: Neuroendocrine regulation of cardiac function involves a population of three types of beta-adrenoceptors (ARs). In various mammalian species, beta1- and beta2-AR stimulation produces an increase in contractility; whereas beta3-AR activation mediates negative inotropic effects. At the moment, nothing is known about the physiological role of beta3-AR in fish. Using an isolated working heart preparation, we show that a beta3-AR selective agonist BRL(37344) (0.1-100 nmol l(-1)) elicits a dose-dependent negative inotropism in the freshwater eel Anguilla anguilla. This effect was insensitive to the beta1/beta2-AR inhibitor nadolol (10 mumol l(-1)), but was blocked by the beta3-AR-specific antagonist SR(59230) (10 nmol l(-1)). The analysis of the percentage of stroke work (SW) variations, in terms of EC(50) values, induced by BRL(37344) alone (10 nmol l(-1)), and in presence of SR(59230) (10 nmol l(-1)), indicated a competitive antagonism of SR(59230). In addition to the classic positive inotropism, the non-specific beta agonist isoproterenol (100 nmol l(-1)) induced, in 30% of the preparations, a negative inotropic effect that was abrogated by pre-treatment with SR(59230), pointing to a beta3-mediated pathway. The BRL(37344)-induced negative inotropic effect was abolished by exposure to a G(i/o) proteins inhibitor pertussis toxin (PTx; 0.01 nmol l(-1)), suggesting a G(i/o)-dependent mechanism. Using L-N5(l-imino-ethyl)ornithine (L-NIO; 10 mumol l(-1)), as a nitric oxide (NO) synthase (NOS) blocker and haemoglobin (Hb; 1 mumol l(-1)), as a NO scavenger, we demonstrated that NO signalling is involved in the BRL(37344)-induced response. Pre-treatment with either an inhibitor of soluble guanylate cyclase (GC) 1H-(1,2,4) oxadiazolo-(4,3-a)quinoxalin-1-one (ODQ; 10 mumol l(-1)), or an inhibitor of the cGMP-activated protein kinase (PKG) KT(5823) (100 nmol l(-1)), abolished the beta3-dependent negative inotropism, indicating the cGMP-PKG component as a crucial target of NO signalling. Taken together, our findings provide functional evidence for the presence of beta3-like adrenoceptors in the eel Anguilla anguilla heart identifying, for the first time in a working fish heart, the beta3-AR-dependent negative inotropy discovered in mammals.
authors.affiliation: Department of Pharmaco-Biology, University of Calabria, 87030, Arcavacata di Rende, CS, Italy.
authors.forename: S
authors.initials: S
authors.lastname: Imbrogno
authors.forename: T
authors.initials: T
authors.lastname: Angelone
authors.forename: C
authors.initials: C
authors.lastname: Adamo
authors.forename: E
authors.initials: E
authors.lastname: Pulerà
authors.forename: B
authors.initials: B
authors.lastname: Tota
authors.forename: M C
authors.initials: MC
authors.lastname: Cerra
mesh_terms: D058667:Adrenergic beta-3 Receptor Agonists; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000811:Anguilla / Q000502:physiology*; D000818:Animals; D006152:Cyclic GMP / Q000378:metabolism*; D017869:Cyclic GMP-Dependent Protein Kinases / Q000378:metabolism; D003864:Depression, Chemical; D004983:Ethanolamines / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism; D006321:Heart / Q000187:drug effects / Q000502:physiology; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D009200:Myocardial Contraction / Q000187:drug effects / Q000502:physiology*; D009248:Nadolol / Q000494:pharmacology; D009569:Nitric Oxide / Q000378:metabolism*; D011412:Propanolamines / Q000494:pharmacology; D022702:Receptors, Adrenergic, beta-3 / Q000502:physiology*; D015398:Signal Transduction
chemical_list: C097869:3-(2-ethylphenoxy)-1-(1,2,3,4-tetrahydronaphth-1-ylamino)-2-propanol oxalate; D058667:Adrenergic beta-3 Receptor Agonists; D000318:Adrenergic beta-Agonists; D000319:Adrenergic beta-Antagonists; D004983:Ethanolamines; D011412:Propanolamines; D022702:Receptors, Adrenergic, beta-3; D009569:Nitric Oxide; D009248:Nadolol; C057368:BRL 37344; D017869:Cyclic GMP-Dependent Protein Kinases; D019204:GTP-Binding Proteins; D006152:Cyclic GMP; D007545:Isoproterenol