Identification of endothelin receptor subtypes in rat kidney cortex using subtype-selective ligands

Area of Science:

• Pharmacology
• Endocrinology
• Renal Physiology

Background:

• Endothelin (ET) receptors play crucial roles in regulating physiological processes, including renal function.
• Understanding the distribution and characteristics of ET receptor subtypes (ETA and ETB) in the kidney is essential for targeted therapeutic interventions.

Purpose of the Study:

• To characterize the binding affinity and density of Endothelin (ET)-1 and ET-3 binding sites in rat kidney cortex membranes.
• To determine the relative proportions of ETA and ETB receptor subtypes in the rat kidney cortex using selective ligands.

Main Methods:

• Radioligand binding assays using radiolabeled 125I-Endothelin (ET)-1 and 125I-ET-3.
• Saturation binding experiments to determine dissociation constants (Kd) and maximum binding (Bmax).
• Competitive binding studies utilizing selective ETA receptor antagonist BQ123 and selective ETB receptor agonist sarafotoxin 6c.

Main Results:

• Both 125I-ET-1 and 125I-ET-3 exhibited specific, saturable, high-affinity binding to rat kidney cortex membranes.
• 125I-ET-3 binding sites were 40-50% less abundant than 125I-ET-1 binding sites.
• Sarafotoxin 6c and BQ123 selectively inhibited binding, indicating the presence of both ETA and ETB receptors in a 50:50 ratio. 125I-ET-1 bound to both subtypes, while 125I-ET-3 primarily bound to ETB receptors.

Conclusions:

• Rat kidney cortex possesses both ETA and ETB receptors in approximately equal proportions.
• 125I-ET-1 demonstrates high-affinity binding to both ETA and ETB receptors.
• 125I-ET-3 shows high-affinity binding predominantly to ETB receptors, and sarafotoxin 6c and BQ123 are effective tools for differentiating ET receptor subtypes in kidney tissue.