Specific binding site for pro atrial natriuretic factors 1-30, 31-67, and 99-126 on distal nephrons, proximal tubules, renal cortical and medullary membranes.

Two peptides with natriuretic and diuretic properties consisting of amino acids (a.a.) 1-30 and 31-67 of the 98 a.a. N-terminal end of the prohormone of atrial natriuretic factor (proANF), which normally circulates in humans and animals, were investigated to determine if they have specific binding sites on distal nephrons, proximal tubules, renal cortical and medullary membranes. Competitive binding experiments revealed that proANFs 1-30, 31-67, and 99-126 (i.e., C-terminus; ANF) each had specific and separate binding sites. The dissociation constants (Kd) for proANFs 1-30, 31-67, and 99-126 binding to renal cortical membranes were similar at 9.8, 5.1, and 4.7 nM, respectively. In renal medullary membranes, on the other hand, proANF1-30 (Kd = 3.7 nM) and proANF31-67 (Kd = 2.9 nM) had a 10-fold higher binding affinity than ANF (Kd = 56 nM). All three peptides had very weak binding to proximal tubules with the respective Kds for proANF1-30, proANF31-67, and ANF of 892, 789, and 550 nM indicating a 50- to 100-fold less affinity for their binding sites in proximal tubules than in distal nephrons (Kds of 4.9, 5.3, and 11 nM, respectively). Each peptide bound to the respective kidney membranes or tubules between 10(-8) and 10(-11) M but could only bind to the other peptides' receptors at concentrations of 10(-6) and 10(-7) M. Neither insulin, growth hormone, nor adrenocorticotrophic hormone competitively inhibited the binding of proANF 1-30, proANF 31-67 or ANF. These results suggest that proANF 1-30 and proANF31-67 do not work through the ANF receptor but rather have their own separate and distinct receptors to mediate their diuretic and natriuretic effects in the kidney.