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The Journal of Experimental Biology 206, 2675-2684 (2003)
doi: 10.1242/jeb.00468

Angiotensin II-induced inotropism requires an endocardial endothelium-nitric oxide mechanism in the in-vitro heart of Anguilla anguilla

Sandra Imbrogno¹, Maria Carmela Cerra^1,2 and Bruno Tota^1,3,*

¹ Department of Cellular Biology, University of Calabria, 87030, Arcavacata di Rende, CS, Italy
² Department of Pharmaco-Biology, University of Calabria, 87030, Arcavacata di Rende, CS, Italy
³ Zoological Station `A. Dohrn', Villa Comunale, 80121 Naples, Italy

^* Author for correspondence (e-mail: tota{at}unical.it)

Accepted 28 April 2003

Using an isolated working heart preparation we show that angiotensin II (ANG II), at concentrations of 10^-10–10^-7 mol l^-1, elicits negative chronotropism and inotropism in the freshwater eel Anguilla anguilla. The negative inotropism was insensitive to losartan and CGP42112 (AT₁ and AT₂ ANG II receptor antagonists, respectively), and was abrogated by the AT₁ receptor antagonist CV11974, the G protein blocker pertussis toxin (PTx) and the muscarinic antagonist atropine. In contrast, it was not affected by the adrenoceptor antagonists propanolol, sotalol and phentolamine. Using donors (L-arginine) and inhibitors [N^G-monomethyl-_L-arginine (L-NMMA), L-N⁵(1-iminoethyl)ornithine (_L-NIO)] of nitric oxide synthase (NOS), and haemoglobin as NO scavenger, we demonstrate that NO signalling is involved in ANG II-mediated inotropism. Pretreatment with Triton X-100, a detergent that damages the endocardial endothelium (EE), or with 1H-(1,2,4)oxadiazolo-(4,3-a)quinoxalin-1-one (ODQ), a specific inhibitor of soluble guanylate cyclase, or with the cGMP-activated protein kinase (PKG) inhibitor KT5328, abolished ANG II-mediated inotropism. Thus, ANG II-mediated inotropism occurs via an EE-NO-cGMP-PKG mechanism. ANG II did not affect the mechanical performance influenced by preload changes (i.e. the Frank–Starling response), which in the eel heart is modulated by NO. This EE-paracrine-mediated cardio-suppressive action of endoluminal ANG II suggests that the hormone plays an important intracardiac role in the fish heart.

Key words: fish heart, angiotensin, nitric oxide, endocardial endothelium, Frank–Starling response, European eel, Anguilla anguilla

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