Multiple forms of atrial natriuretic factor receptor in human placenta

Multiple forms of atrial natriuretic factor receptor have been identified in human placental membranes. Atrial natriuretic factor binds specifically to placental membranes and the binding activity could be solubilized using non ionic detergent, Triton X-100. Binding to the detergent solubilized preparation was inhibited 80% by the addition of 0.5 M sodium chloride. Affinity cross-linking analysis indicated that this binding was associated with a single protein band of molecular weight 170-kDa. On the other hand, if sodium chloride was added together with a chelator, o-phenanthroline, ANF binding to this preparation was stimulated 300%. Binding under these conditions was not to the 170-kDa protein but was associated with a broad band in the region of 100/110-kDa and a minor band at 200-kDa. These observations clearly indicated that in human placental membranes, atrial natriuretic factor binds to distinctly different molecular species depending on the presence or absence of certain ions and chelators. The two types of binding could be conveniently assayed in the presence of each other by elimination or inclusion of sodium chloride and o-phenanthroline in the assay system.