Morphological and physiological study of the cardiac NOS/NO system in the Antarctic (Hb/Mb) icefish Chaenocephalus aceratus and in the red-blooded Trematomus bernacchii

The nitric oxide synthase (NOS)/nitric oxide (NO) system integrates cellular biochemical machinery andenergetics. In heart microenvironment, dynamic NO behaviour depends upon the presence of superoxideanions, haemoglobin (Hb), and myoglobin (Mb), being hemoproteins are major players disarming NO bioactivity.The Antarctic icefish, which lack Hb and, in some species, also cardiac Mb, represent a uniquemodel for exploring Hb and Mb impact on NOS/NO function. We report in the (Hb/Mb) icefish Chaenocephalusaceratus the presence of cardiac NOSs activity (NADPH-diaphorase) and endothelial NOS (eNOS)/inducible NOS (iNOS) zonal immuno-localization in the myocardium. eNOS is localized on endocardiumand, to a lesser extent, in myocardiocytes, while iNOS is localized exclusively in myocardiocytes. ConfrontingeNOS and iNOS expression in Trematomus bernacchii (Hb+/Mb+), C. hamatus (Hb/Mb+) and C. aceratus(Hb/Mb) is evident a lower expression in the Mb-less icefish.NO signaling was analyzed using isolated working heart preparations. In T. bernacchii, L-arginine andexogenous (SIN-1) NO donor dose-dependently decreased stroke volume, indicating decreased inotropism.L-arginine-induced inotropism was NOSs-dependent, being abolished by NOSs-inhibitor NG-monomethyl-L-arginine (L-NMMA). A SIN-1-induced negative inotropism was found in presence of SOD. NOSinhibition by L-N5-N-iminoethyl-L-ornithine (L-NIO) and L-NMMA confirmed the NO-mediated negativeinotropic influence on cardiac performance. In contrast, in C. aceratus, L-arginine elicited a positive inotropism.SIN-1 induced a negative inotropism, which disappeared in presence of SOD, indicating peroxynitriteinvolvement. Cardiac performance was unaffected by L-NIO and L-NIL. NO signaling acted via acGMP-independent mechanism. This high conservation degree of NOS localization pattern and signalinghighlights its importance for cardiac biology.