Neuroendocrine regulation of cardiac function involvesa population of three types of -adrenoceptors (ARs). Invarious mammalian species, 1- and 2-AR stimulationproduces an increase in contractility; whereas 3-ARactivation mediates negative inotropic effects. At themoment, nothing is known about the physiological role of3-AR in fish.Using an isolated working heart preparation, we showthat a 3-AR selective agonist BRL37344 (0.1–100·nmol·l–1)elicits a dose-dependent negative inotropism in thefreshwater eel Anguilla anguilla. This effect was insensitiveto the 1/2-AR inhibitor nadolol (10·mol·l–1), butwas blocked by the 3-AR-specific antagonist SR59230(10·nmol·l–1). The analysis of the percentage of strokework (SW) variations, in terms of EC50 values, induced byBRL37344 alone (10·nmol·l–1), and in presence of SR59230(10·nmol·l–1), indicated a competitive antagonism ofSR59230. In addition to the classic positive inotropism, thenon-specific agonist isoproterenol (100·nmol·l–1) induced,in 30% of the preparations, a negative inotropic effect thatwas abrogated by pre-treatment with SR59230, pointing to a3-mediated pathway. The BRL37344-induced negative inotropic effect was abolished by exposure to a Gi/oproteins inhibitor pertussis toxin (PTx; 0.01·nmol·l–1),suggesting a Gi/o-dependent mechanism. Using L-N5(limino-ethyl)ornithine (L-NIO; 10·mol·l–1), as a nitricoxide (NO) synthase (NOS) blocker and haemoglobin (Hb;1·mol·l–1), as a NO scavenger, we demonstrated that NOsignalling is involved in the BRL37344-induced response.Pre-treatment with either an inhibitor of soluble guanylatecyclase (GC) 1H-(1,2,4) oxadiazolo-(4,3-a)quinoxalin-1-one(ODQ; 10·mol·l–1), or an inhibitor of the cGMP-activatedprotein kinase (PKG) KT5823 (100·nmol·l–1), abolished the3-dependent negative inotropism, indicating the cGMPPKGcomponent as a crucial target of NO signalling.Taken together, our findings provide functional evidencefor the presence of 3-like adrenoceptors in the eelAnguilla anguilla heart identifying, for the first time in aworking fish heart, the 3-AR-dependent negativeinotropy discovered in mammals.
Beta3-Adrenoceptor in the eel (Anguilla anguilla) heart: negative inotropy and NO-cGMP-dependent mechanism
IMBROGNO, Sandra;ANGELONE, Tommaso;CERRA, Maria Carmela
2006-01-01
Abstract
Neuroendocrine regulation of cardiac function involvesa population of three types of -adrenoceptors (ARs). Invarious mammalian species, 1- and 2-AR stimulationproduces an increase in contractility; whereas 3-ARactivation mediates negative inotropic effects. At themoment, nothing is known about the physiological role of3-AR in fish.Using an isolated working heart preparation, we showthat a 3-AR selective agonist BRL37344 (0.1–100·nmol·l–1)elicits a dose-dependent negative inotropism in thefreshwater eel Anguilla anguilla. This effect was insensitiveto the 1/2-AR inhibitor nadolol (10·mol·l–1), butwas blocked by the 3-AR-specific antagonist SR59230(10·nmol·l–1). The analysis of the percentage of strokework (SW) variations, in terms of EC50 values, induced byBRL37344 alone (10·nmol·l–1), and in presence of SR59230(10·nmol·l–1), indicated a competitive antagonism ofSR59230. In addition to the classic positive inotropism, thenon-specific agonist isoproterenol (100·nmol·l–1) induced,in 30% of the preparations, a negative inotropic effect thatwas abrogated by pre-treatment with SR59230, pointing to a3-mediated pathway. The BRL37344-induced negative inotropic effect was abolished by exposure to a Gi/oproteins inhibitor pertussis toxin (PTx; 0.01·nmol·l–1),suggesting a Gi/o-dependent mechanism. Using L-N5(limino-ethyl)ornithine (L-NIO; 10·mol·l–1), as a nitricoxide (NO) synthase (NOS) blocker and haemoglobin (Hb;1·mol·l–1), as a NO scavenger, we demonstrated that NOsignalling is involved in the BRL37344-induced response.Pre-treatment with either an inhibitor of soluble guanylatecyclase (GC) 1H-(1,2,4) oxadiazolo-(4,3-a)quinoxalin-1-one(ODQ; 10·mol·l–1), or an inhibitor of the cGMP-activatedprotein kinase (PKG) KT5823 (100·nmol·l–1), abolished the3-dependent negative inotropism, indicating the cGMPPKGcomponent as a crucial target of NO signalling.Taken together, our findings provide functional evidencefor the presence of 3-like adrenoceptors in the eelAnguilla anguilla heart identifying, for the first time in aworking fish heart, the 3-AR-dependent negativeinotropy discovered in mammals.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
