Related Experiment Videos
The kappa opioid receptor expressed on the mouse R1.1 thymoma cell line down-regulates without desensitizing during
1Department of Pharmacology, University of Rochester, School of Medicine and Dentistry, New York.
Abstract:
The R1.1 mouse thymoma cell line expresses a single class of kappa opioid receptors that is negatively coupled to adenylyl cyclase through a Bordetella pertussis toxin-sensitive inhibitory guanine nucleotide-binding protein. The aim of the present study was to determine whether chronic opioid treatment of R1.1 cells altered either the binding properties or the functional response associated with the kappa opioid receptor. Culturing of R1.1 cells with the kappa-selective agonist (trans)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)-cyclohexyl] benzeneacetamide methane-sulfonate hydrate (U50,488) for 3 hr and longer, followed by extensive washing of R1.1 cell membranes, produced a concentration- and time-dependent reduction in the binding of the kappa-selective ligand (5 alpha,7 alpha,8 beta)-(-)-N-methyl-N-(7-(1-pyrrolidinyl)-1- oxaspiro(4,5)dec-8-yl) benzeneacetamide ([3H]U69,593). Culturing of R1.1 cells with 100 nM U50,488 for 24 hr produced approximately a 50% reduction in the Bmax value for [3H]U69,593 and [3H]naloxone binding. In contrast to the reduction in binding, there was no change in the inhibition of adenylyl cyclase activity by (-)-U50,488. To determine whether kappa opioid receptor function was maintained by spare receptors after agonist-induced down-regulation, membranes from untreated R1.1 cells were incubated with 400 nM of the irreversible opioid antagonist beta-chlornaltrexamine (beta-CNA) followed by extensive washing. beta-CNA produced a 50% reduction in the [3H]U69,593 binding and a 6-fold increase in the IC50 value for (-)-U50,488 inhibition of adenylyl cyclase activity, with no change in the maximal inhibition of cyclic AMP levels.(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
Chronic kappa opioid agonist treatment of R1.1 cells reduced kappa opioid receptor binding but did not alter receptor function, suggesting spare receptors maintain adenylyl cyclase inhibition despite down-regulation.
Area of Science:
- Pharmacology
- Cell Biology
- Neuroscience
Background:
- R1.1 mouse thymoma cells possess kappa opioid receptors coupled to adenylyl cyclase via a pertussis toxin-sensitive G protein.
- Understanding opioid receptor regulation is crucial for developing targeted therapeutics.
Purpose of the Study:
- To investigate the effects of chronic kappa opioid agonist treatment on kappa opioid receptor binding and function in R1.1 cells.
- To determine if spare receptors contribute to maintaining receptor function after agonist-induced down-regulation.
Main Methods:
- R1.1 cells were cultured with a kappa-selective agonist (U50,488) to induce receptor down-regulation.
- Radioligand binding assays ([3H]U69,593, [3H]naloxone) were performed to assess receptor density (Bmax).
- Adenylyl cyclase activity assays were used to measure functional responses to the agonist.
- Irreversible antagonist (beta-chlornaltrexamine) was used to probe receptor reserve.
Main Results:
- Chronic U50,488 treatment led to a concentration- and time-dependent decrease in kappa opioid receptor binding.
- A 24-hour incubation with U50,488 reduced the Bmax for [3H]U69,593 and [3H]naloxone binding by approximately 50%.
- Despite reduced binding, the inhibition of adenylyl cyclase activity by U50,488 remained unchanged.
- Treatment with beta-chlornaltrexamine reduced receptor binding and increased the agonist's IC50 for adenylyl cyclase inhibition, but maximal inhibition was preserved.
Conclusions:
- Chronic kappa opioid agonist exposure down-regulates kappa opioid receptors in R1.1 cells, primarily affecting receptor binding capacity.
- The functional response (adenylyl cyclase inhibition) is maintained despite receptor down-regulation, indicating the presence of spare receptors.
- These findings highlight the complex mechanisms of opioid receptor regulation and the role of receptor reserve in maintaining cellular signaling.