engleski

Chronic opioid treatment leads to down-regulation of kappa-opioid receptor without desensitizing mouse thymoma cell lines

It was demonstrated that k-opioid agonists alter functions of macrophages, polymorphonuclear cells, T and B lymphocytes. Also, there is evidence that mouse thymoma cell lines R1.G1 and R1EGO express only k-opioid receptors that are coupled to Gi, a pertussis-toxin sensitive protein. The R1.G1 and R1EGO cells, available from ATCC, were treated acutely (15 min) and chronically (24 hrs) with a k-opioid agonist (-)U50, 488 (100 nM). After treatment membranes were prepared and used for experiments. (^3H)U69, 593 was used for saturation binding experiments to determine Kd (dissociation constant) and Bmax values (receptor number), while adenylyl-cyclase activity was measured by modified RIA kit. Bmax values for R1.G1 cell line were 266 fmol/mg protein (15 min) and 142 fmol/mg proteins (24 hrs) and for R1EGO cell line 250 fmol/mg proteins (15 min) and 149 fmol/mg proteins (24 hrs). The Kd was for R1.G1 cell line 2.00 nM (15 min) and 2.13 nM (24 hrs), and for R1EGO cell line 1.90 nM (15 min) and 2.40 nM (24 hrs). There was no significant difference in the rate of inhibition of adenylyl-cyclase activity between the acute and chronic treatment in both cell lines using titration range 0.11 pmol - 27 pmol (-)U50.488. Chronic opioid treatment of R1.G1 and R1EGO cell lines lead to down-regulation, decrease of Bmax for approximately 50%, however binding affinity was not affected significantly in both cell lines. The rate of inhibition of adenylyl-cyclase activity was not altered after chronic treatment. Thus, chronic treatment with k-opioid agonist leads to down-regulation of the k-opioid receptor without desensitizing the receptor on mouse thymoma cell lines.

kappa-opioid receptors ; thymomas ; adenylyl cyclase

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