A QUANTITATIVE AUTORADIOGRAPHIC STUDY OF I-125 ATRIAL-NATRIURETIC-FACTOR IN THE HEART OF A TELEOST FISH (CONGER-CONGER)

Quantitative receptor autoradiographic study of I-125-atrial natriuretic peptide factor (ANF) in the heart of a teleost fish Conger conger has shown that a heterogenous distribution of I-125-ANF binding exists in the different cardiac regions. Elevated ANF binding densities (3,790 fmol/mg protein) were encountered in the innermost layer (tunica intima) of the bulbus arteriosus while lower binding levels (293-403 fmol/mg protein) were revealed in atrium and ventricle. In order to determine I-125-ANF binding characteristics (K(D), B(max)) in the above cardiac sites, saturation binding assays were carried out. The results show that low I-125-ANF K(D) values (28.8-52.6 pM) were found in the atrium and in the bulbus arteriosus with respect to the higher K(D) values (373 pM) of the ventricle. The number of binding sites were respectively 632 and 1,279 fmol/mg protein for the atrium and the ventricle, while a substantially elevated B(max) of 7,235 fmol/mg protein was found for the bulbus arteriosus. These results may furnish some insights concerning ANF receptor binding activity and its putative regulatory role of different cardiac functions.