Atrial natriuretic factor binding sites in the jejunum

Area of Science:

• Gastroenterology
• Endocrinology
• Cell Biology

Background:

• Atrial natriuretic factor (ANF) plays a role in cardiovascular and renal functions.
• The presence and function of ANF receptors in the gastrointestinal tract are not fully understood.

Purpose of the Study:

• To investigate the localization and pharmacological characteristics of ANF binding sites in the rat jejunum.
• To determine the specific cell types expressing ANF receptors in the jejunal villi.

Main Methods:

• Quantitative in vitro radioautography using 125I-ANF-(99-126) on rat jejunum sections.
• Computerized microdensitometry for analyzing binding site density and affinity (Kd, Bmax).
• In vivo electron microscope radioautography to identify cellular localization of binding sites.

Main Results:

• High-affinity, low-capacity ANF binding sites were detected in rat jejunal villi (Kd=48 pM, Bmax=63 fmol/mg protein).
• Competition studies confirmed the specificity of ANF binding, with ANF-(99-126) being more potent than ANF-(103-123).
• Electron microscopy revealed ANF binding sites predominantly on lamina propria fibroblast-like cells (80%), with smaller amounts on enterocytes (18%) and capillaries (2%).

Conclusions:

• The rat jejunum possesses specific ANF binding sites with pharmacological properties consistent with functional ANF receptors.
• These receptors are primarily located on fibroblast-like cells within the jejunal villi.
• This study elucidates the presence and cellular distribution of ANF receptors in the rat small intestine, suggesting potential roles in intestinal function.