Identification and Localization of Atrial Natriuretic Factor Receptors in Human Spermatozoa

Abstract

Specific binding sites for atrial natriuretic factor (ANF) have been detected and localized in viable human spermatozoa through radioreceptor analysis and autoradiography, respectively. Radiotracer uptake was time and concentration dependent. Scatchard analysis of saturation data showed a single class of ANF receptors with a k_d of 2.5 nM and a B_max of 1.03 fmol/10 sperm 2.5 min⁻¹, corresponding to about 620 molecules per sperm. Nonreducing SDS-PAGE analysis after covalent cross-linking of sperm bound ¹²⁵I-ANF evidenced a single displaceable (i.e., specific) band with an apparent molecular weight of 135–140k^D. In ¹²⁵I-ANF bound spermatozoa, optical autoradiography showed an exclusive distribution of silver grains covering the midpiece region. The effects of ANF binding on ionic homeo-stasis and cyclic nucleotide metabolism, which modulate a number of sperm cellular processes, could make this factor play outstanding roles in gamete physiology.

Key Words:

• ANF receptor
• Human spermatozoa
• Autoradiography.