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

• Published in: Journal of Experimental Biology
• Main Authors: Pellegrino, D., Palmerini, C. A., Tota, B.
• Format: Text
• Language: English
• Published: Company of Biologists 2004
• Subjects: Research Article; Antarctic; Antarc*; Icefish
• Online Access: http://jeb.biologists.org/cgi/content/short/207/22/3855; https://doi.org/10.1242/jeb.01180

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 (<scp>l</scp>-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. <scp>l</scp>-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.