AJP - Regulatory, Integrative and Comparative Physiology, Vol 263, Issue 4 747-R755, Copyright © 1992 by American Physiological Society
Atrial natriuretic factor binding sites in rat area postrema: autoradiographic study
E. M. Konrad, G. Thibault and E. L. Schiffrin
Laboratory of Pathobiology, Clinical Research Institute of Montreal, Quebec, Canada.
The area postrema (AP) is a brain stem circumventricular organ implicated,
among other functions, in central cardiovascular (CV) regulation.
Competition binding analysis performed by quantitative in vitro
autoradiography demonstrated specific, high-affinity (Kd, 0.32 +/- 0.11
nM), low-capacity (Bmax, 57.5 +/- 10.9 fmol/mg protein) atrial natriuretic
factor (ANF) binding sites in the AP. C-ANF
[des-(Gln116-Gly120)ANF-(Arg102-Cys121)-NH2] and ANF-(Phe106-Ile113)-NH2
(two ligands endowed with selectivity for the ANF-C receptor), as well as
C-type natriuretic peptide (CNP), did not compete noticeably at
pathophysiological concentrations for 125I-ANF binding. 125I-[Tyr0]CNP
bound to the AP to a much lower extent than 125I-ANF. Electron microscopic
autoradiography in vivo disclosed that 125I-ANF was preferentially bound to
axon, dendrite, and astrocyte plasmalemma. These studies demonstrate that
the AP contains natriuretic peptide binding sites with pharmacological
characteristics of the ANF-A and ANF-B but not of the ANF-C receptor
subtype. In the AP, ANF interacts with those sites resembling ANF-A
receptors. Cellular localization of these binding sites may relate to their
possible involvement in the centrally mediated salt and water regulation
and/or CV effects of circulating ANF.
