MULTIPLE TYPES OF BINDING-SITES FOR ATRIAL-NATRIURETIC-PEPTIDE IN RATOLFACTORY-BULB MEMBRANES AND SYNAPTOSOMES

The binding of atrial natriuretic peptide (ANP) to rat olfactory bulb membranes and synaptosomes was examined. [I-125]ANP (rat, 99-126) boun d specifically to a single class of binding site on olfactory bulb mem brane preparation with dissociation constant (K-d) of 106 pM and maxim um binding capacity (B-max) of 13.6 fmol/mg protein. Comparable result s were obtained when the binding was characterized using displacement and kinetic experiments. The ring deleted analog of ANP, C-ANP (rat, 4 -23) displaced [I-125]ANP only minimally from its binding site in the membrane preparation. Saturation, displacement and blocking experiment s on [I-125]ANP binding to rat olfactory bulb synaptosomes revealed th e presence of two distinct binding sites. Simultaneous analysis of hom ogeneous and heterogeneous displacement curves and blocking experiment s revealed the quantitative characteristics of these receptors to be: K-d1 = 44 pM, B-max1 = 42 fmol/mg protein and K-d2 = 1050 pM, B-max2 = 173 fmol/mg protein, for the high and low affinity binding sites, res pectively. Kinetic experiments further confirmed the differences betwe en the receptors present in the membranes and the synaptosomes prepara tions. The demonstration of multiple ANP binding sites in olfactory bu lb synaptosomes but not membrane preparations raises the possibility o f a particular function of ANP in nerve terminals.