Absence of C-Type Natriuretic Peptide Receptors in Hamster Glomeruli

Abstract

The distribution of atrial natriuretic peptide receptor B (ANPR-B) varies between tissues and species. The aim of this study is to determine whether ANPR-B is present in the hamster glomeruli. In vitro C-type natriuretic peptide (CNP)- and atrial natriuretic factor (ANF)-stimulated cGMP accumulation studies were performed in hamster glomeruli. Elevated cGMP accumulations were observed upon ANF addition. No cGMP response was seen with CNP. Competitive receptor-binding experiments were performed with ¹²⁵I-CNP and ¹²⁵I-ANF against their respective cold peptides in hamster glomeruli. Although no CNP binding was detected, positive ANF binding was found and two types of ANF receptor were demonstrated. The affinity (K_d1) and maximum binding capacity (B_max1) of the high-affinity ANF receptor were 0.014 ± 0.001 nMand 60.4 ± 10.2 fmol/mg protein, respectively. Those of the low-affinity receptor (K_d2 and B_max2) were 45.7 ± 6.2 n M and 28.3 ± 6.3 pmol/mg protein, respectively. Similarly, saturation binding experiments also failed to show any CNP receptor binding in hamster glomeruli. This finding suggests that ANPR-B is not present in hamster glomeruli and CNP is not a direct physiological regulator of hamster renal function.