Angiotensin II binding sites in the heart of Scyliorhinus canicula: An autoradiographic study

Dogfish I-125 [Asn(1), Pro(3), Ile(5)] angiotensin II (I-125 dfANG II) was used to establish the specific binding patterns of the different cardiac re gions of the elasmobranch Scyliorhinus canicula by in vitro autoradiography . In the ventricular myocardium Scatchard analysis of saturation and displa cement binding data revealed two classes of high- and low-affinity dfANG II binding sites (K-d = 53 +/- 10 and 1300 +/- 900 pM). Two classes of dfANG II binding sites were also detected in the atrium (K-d = 47 +/- 13 and 4690 +/- 930 pM) and in the outer layer of the conus arteriosus (K-d = 16 +/- 9 and 398 +/- 83 pM). Conversely, the ventricular endocardium and the inner conal layer were characterized by a single class of dfANG II binding sites with affinity values of 48 +/- 11 and 106 +/- 3.3 pM, respectively. Competi tion experiments with either cold dfANG II or CV11974 or CGP42112 (specific ligands for mammalian AT(1) and AT(2) receptors, respectively) demonstrate d a prevalence of CGP42112-selective dfANG II binding sites in both the inn er and the outer conal layers. In the atrium, the ventricular myocardium, a nd the outer conal layer, dfANG II high-affinity binding sites poorly discr iminated among the cold ligands. These results suggest that the dogfish hea rt may be a target organ of ANG II with distinct ANG II receptor subtype di stributions. (C) 2001 Academic Press.