ATRIAL-NATRIURETIC-FACTOR RECEPTOR SUBTYPES IN THE RAT CENTRAL-NERVOUS-SYSTEM

In this study we investigated the presence and anatomical location of atrial natriuretic factor (ANF) receptor subtypes in the rat central nervous system using in vitro autoradiographic and cross-linking techniques. I-125-ANF-(Ser99-Tyr126) served as a labeled ligand, whereas ANF-(Ser99-Tyr126) and two peptides endowed with selectivity for ANF-C receptor-namely, C-ANF (des-[Gln116-Gly120] ANF-[Asp102-Cys121]-NH2) and ANF-(Phe106-Ile113)-NH2-were used as displacing agents. Distribution studies revealed the presence of specific ANF binding sites in a number of central nervous system areas examined. C-ANF at 10(-6) M competed for I-125-ANF binding to a much lower extent than ANF in many of those structures, whereas ANF-(106-113)-NH2 at 10(-6) M did not have a significant effect on the radioligand binding except in the choroid plexus, pia-arachnoid, and olfactory bulb. Analysis of the competition curves revealed that in the choroid plexus, pia-arachnoid, olfactory bulb, subfornical organ, area postrema, and habenular nucleus, ANF interacts with its binding sites with high affinity (IC50, 0.46-0.77 nM). In contrast, C-ANF and ANF-(106-113)-NH2 competed for I-125-ANF binding with high potency (IC50, 2-16 nM) in the choroid plexus and pia-arachnoid only, where they were able to displace 60-70% of the radioligand binding. I-125-ANF cross-linking to olfactory bulb membranes resolved a specific 120-kDa band corresponding to the high molecular weight receptor but did not disclose a specifically labeled band corresponding to the low molecular mass receptor. Therefore, these studies revealed the presence of ANF binding sites with the characteristics of ANF-C receptors in the choroid plexus and pia-arachnoid but not in other central nervous system structures.