Aortic smooth muscle contains guanylate-cyclase-coupled 130-kDa atrial natriuretic factor receptor as predominant receptor form. Spontaneous switching to 60-kDa C-receptor upon cell culturing

Photoaffinity labeling of atrial natriuretic factor (ANF) receptor in the plasma membranes from bovine aortic smooth muscle tissue using N alpha 5-(4-azidobenzoyl)-ANF-(5-28)- peptide labeled with 125I yielded a 130-kDa band. However, when smooth muscle cells from the same bovine aorta were placed in culture, the 130-kDa receptor quickly disappeared and a 60-kDa band began to appear at high density. After three passages, essentially no 130-kDa band was found and only the 60-kDa band was strongly labeled. The primary structures of the two receptor forms were compared by radiochemical peptide mapping after endoproteinase Glu-C digestion of photoaffinity-labeled and detergent-solubilized 130-kDa receptor from the aorta or the 60-kDa receptor from the cultured cells. The peptide mapping showed courses of digestion that were significantly different from each other, suggesting difference in their primary structures. The basal guanylate cyclase activity in the aortic membranes was 1.0 pmol cGMP produced.min-1.mg protein-1 at 37 degrees C using Mn(2+)-GTP as substrate. The corresponding activity in the membranes from the cultured cells was 20 fmol cGMP.min-1.mg protein-1. Binding studies gave a density of binding sites (Bmax) of 82 fmol/mg protein for the aortic membranes and 850 fmol/mg protein for the cultured cell membranes. These data suggest that the major form of ANF receptor in the cultured cells, namely the 60-kDa receptor, lacked guanylate cyclase activity. Northern blot analysis of poly(A)-RNA extracted form bovine thoracic aorta or adrenal cortex gave a single 3.6-kb band when 32P-labeled human A-type ANF receptor cDNA was used as a hybridization probe. However, no band was detected when C-receptor cDNA was used as a probe. In addition to the major 130-kDa band, extended SDS/PAGE revealed two additional faint bands with estimated molecular masses of 126 kDa and 135 kDa. Treatment with endoglycosidase H resulted in disappearance of the 126-kDa band and appearance of a 100-kDa band. The 130-kDa and 135-kDa bands were unchanged. Treatment by endoglycosidase F or glycopeptidase F reduced all three bands to a single 100-kDa band. These results suggest that the slight difference in mobility is due to different states of glycosylation.(ABSTRACT TRUNCATED AT 400 WORDS)

[Regulation of V1-vasopressinergic receptors in the rat]

Using tritiated vasopressin, specific binding sites for vasopressin were identified on splenic membranes of Sprague-Dawley rats. One class of high affinity receptors was characterized with an equilibrium dissociation constant of 1.91 +/- 0.16 nM and a maximal binding capacity of 110 +/- 11 fmol/mg of protein. Several experimental evidences suggest that these receptors belong to the V1-vascular type: The affinity of 8 vasopressin agonists for the receptor is correlated to their vasopressor activity in vivo whereas no such relationship exists when their antidiuretic activity is considered. The affinity of 5 vasopressin antagonists for the receptor is correlated to their antivasopressor activity in vivo whereas no such relationship exists when their antidiuretic activity is considered. Vasopressin does not stimulate cyclic AMP production of splenic membranes. The regulation of these receptors was studied in sodium-sensitive (S) and sodium-resistant animals (R) of Dahl receiving a special diet (0.1 or 8% NaCl) for two weeks. In both strains of animals, the number of receptors is smaller in R animals than in S animals, whatever the diet ingested. Splenic membranes of rat bear easily accessible V1-vasopressinergic receptors. These receptors are modulated by sodium intake and the difference in receptor number between S and R rats could explain the increased vascular reactivity of S animals to vasopressin.

Inhibition of aldosterone production by an atrial extract

Crude extracts of rat atria reduced the basal amount of aldosterone released from rat zona glomerulosa cells and partially inhibited aldosterone stimulation by adrenocorticotropic hormone and angiotensin II. The destruction of this activity by trypsin suggests that the active factor is a peptide, possibly atrial natriuretic factor. These data suggest that atrial natriuretic factor affects sodium excretion by the kidneys both directly and through the inhibition of aldosterone production.