DIFFERENT BINDING ACTIVITIES OF A-TYPE AND B-TYPE NATRIURETIC HORMONES IN THE HEART OF 2 ANTARCTIC TELEOSTS, THE RED-BLOODED TREMATOMUS-BERNACCHII AND THE HEMOGLOBINLESS CHIONODRACO-HAMATUS

Different binding activities of I-125-rat atrial natriuretic peptide w ere evaluated using in vitro quantitative autoradiography in the heart of two antarctic notothenioid teleosts, the red-blooded Trematomus be rnacchii and hemoglobinless Chionodraco hamatus. Saturable and specifi c binding sites for rat atrial natriuretic peptide were found in the a trium, ventricular myocardium, ventricular endocardium and inner and o uter layers of the bulbus arteriosus of both fishes. Scatchard analysi s of the saturation data showed that the atrium, ventricular endocardi um and outer bulbar layer of T. bernacchii were characterized by a sin gle class of high affinity natriuretic peptide binding sites (K-d = 14 +/- 3.2, 9.7 +/- 2.3 and 6.2 +/- 1.3 pM, respectively), whereas the v entricular myocardium and the inner bulbar layer contained elevated nu mbers of two classes of high and low affinity natriuretic peptide bind ing sites (1.8 +/- 0.6 < K-d < 209 +/- 66 pM). In contrast, in C. hama tus, both high and low affinity binding sites were detected in all car diac regions (2.1 +/- 0.7 < K-d < 262 +/- 90 pM) In both fishes, compe tition experiments in the presence of either unlabeled rat atrial natr iuretic peptide or porcine brain natriuretic peptide indicated differe nt displacement capacities. Porcine brain natriuretic peptide, able to bind to natriuretic peptides sites in all the heart regions of both n otothenioids, provided a higher displacement capacity with respect to that of rat atrial natriuretic peptide in the atrium of T. bernacchii. (C) Elsevier Science Inc.