Endothelin receptor agonists and antagonists exhibit different dissociation characteristics

Area of Science:

• Pharmacology
• Molecular Biology
• Biochemistry

Background:

• Endothelins (ETs) are peptides that regulate physiological functions through membrane receptors.
• Understanding the binding and dissociation kinetics of ET receptor ligands is crucial for drug development.

Purpose of the Study:

• To compare the dissociation characteristics of endothelin receptor agonists and antagonists.
• To investigate how these differences impact antagonist potency over time.

Main Methods:

• Competition binding assays using radiolabeled ET-1 and ET-3 on porcine cerebellum membranes (predominantly ETB receptors).
• Time-dependent association studies with [125I]IRL1620.
• Bind-and-wash experiments with unlabeled ligands followed by washing and [125I]ET-1 binding assay.
• Studies on cloned human ETA and ETB receptors.

Main Results:

• Both radiolabeled and unlabeled ET receptor agonists (ET-1, ET-3, IRL1620) exhibited slow dissociation from ETB receptors (half-life > 20 h).
• Antagonists PD142893 and Ro46-2005 showed rapid dissociation from ETB receptors.
• The reduced dissociation rate of agonists correlated with sustained binding, while rapid antagonist dissociation led to diminished inhibitory effects over incubation time.

Conclusions:

• Differences in dissociation kinetics between ET receptor agonists and antagonists significantly influence antagonist potency.
• Rapid dissociation of antagonists like PD142893 and Ro46-2005 explains their decreased efficacy with longer incubation periods.
• These findings highlight the importance of considering ligand dissociation rates in the design and evaluation of endothelin receptor modulators.