Related Experiment Videos
A comparison of microsomal and synaptic delta site binding kinetics
J W Spain1, D E Petta, C J Coscia
1E.A. Doisy Department of Biochemistry, St. Louis University School of Medicine, MO 63104.
NIDA Research Monograph
|January 1, 1986
Summary
High-affinity binding of opioid agonists to brain membranes involves multiple steps. However, microsomal binding sites show faster dissociation kinetics and reduced sensitivity to guanine nucleotides compared to synaptic plasma membranes.
Area of Science:
- Neuroscience
- Biochemistry
- Pharmacology
Background:
- Opioid receptors, specifically delta sites, mediate various physiological processes.
- Agonist binding kinetics provide insights into receptor-ligand interactions and downstream signaling.
- Synaptic plasma membranes (SPMs) and internal microsomal membranes may contain distinct receptor populations.
Purpose of the Study:
- To investigate the kinetic differences in high-affinity agonist binding between bovine hippocampal synaptic plasma membranes (SPMs) and microsomal membranes.
- To characterize the formation and dissociation of high-affinity agonist-receptor complexes in these membrane fractions.
- To assess the influence of guanine nucleotides on agonist binding kinetics in SPMs versus microsomes.
Main Methods:
- Utilized radioligand binding assays with [3H]D-ala2-D-leu5-enkephalin (DADLE) as the agonist.
- Performed kinetic analysis to determine association and dissociation rates of DADLE binding to SPMs and microsomes.
- Investigated the effect of guanine nucleotide analogs, such as Gpp(NH)p, on agonist dissociation.
Main Results:
- High-affinity binding of DADLE to SPMs exhibits a multi-step association process.
- Microsomal binding sites showed no association time-dependent dissociation rate, indicating faster dissociation kinetics.
- The slowly dissociating high-affinity complex, prominent in SPMs and sensitive to guanine nucleotides, was minimally formed in microsomes.
- Guanine nucleotide effects on dissociation were significantly reduced for microsomal binding sites.
Conclusions:
- Bovine hippocampal SPMs and microsomal membranes possess distinct delta opioid binding sites with differing kinetic properties.
- The formation of a slowly dissociating, high-affinity agonist-receptor complex, modulated by guanine nucleotides, is characteristic of SPMs but not microsomes.
- These findings suggest functional heterogeneity of opioid binding sites across different cellular membrane compartments.