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First published online October 7, 2004
Journal of Experimental Biology 207, 3855-3864 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.01180

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No hemoglobin but NO: the icefish (Chionodraco hamatus) heart as a paradigm

D. Pellegrino^1,2, C. A. Palmerini³ and B. Tota^2,4,*

¹ Department of Pharmaco-Biology, University of Calabria, 87030, Arcavacata di Rende, CS, Italy
² Department of Cellular Biology, University of Calabria, 87030, Arcavacata di Rende, CS, Italy
³ Department of Cellular and Molecular Biology, University of Perugia, 06126, Perugia, Italy
⁴ Zoological Station `A. Dohrn', Villa Comunale, 80121, Napoli, Italy

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

Accepted 13 July 2004

The role of nitric oxide (NO) in cardio-vascular homeostasis is now known to include allosteric redox modulation of cell respiration. An interesting animal for the study of this wide-ranging influence of NO is the cold-adapted Antarctic icefish Chionodraco hamatus, which is characterised by evolutionary loss of hemoglobin and multiple cardio-circulatory and subcellular compensations for efficient oxygen delivery. Using an isolated, perfused working heart preparation of C. hamatus, we show that both endogenous (L-arginine) and exogenous (SIN-1 in presence of SOD) NO-donors as well as the guanylate cyclase (GC) donor 8Br-cGMP elicit positive inotropism, while both nitric oxide synthase (NOS) and sGC inhibitors, i.e. L-NIO and ODQ, respectively, induce significant negative inotropic effects. These results therefore demonstrate that under basal working conditions the icefish heart is under the tonic influence of a NO-cGMP-mediated positive inotropism. We also show that the working heart, which has intracardiac NOS (shown by NADPH-diaphorase activity and immunolocalization), can produce and release NO, as measured by nitrite appearance in the cardiac effluent. These results indicate the presence of a functional NOS system in the icefish heart, possibly serving a paracrine/autocrine regulatory role.

Key words: nitric oxide, heart, Antarctic teleost, icefish, Chionodraco hamatus, myocardial performance, nitric oxide synthase (NOS), immunocytochemistry

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