Pharmacological characterization of KT-90 using cloned mu-, delta- and kappa-opioid receptors.
We analyzed the pharmacological characteristics of (-)-3-acetyl-6 beta-acetylthio-N-cyclopropylmethyl-normorphine (KT-90) using Chinese hamster ovary (CHO) cells expressing cloned rat mu-, delta- and kappa-opioid receptors. KT-90 displaced the specific binding of the following radiolabeled ligands selective to the mu-, delta- and kappa-opioid receptors, [3H][D-Ala2,MePhe4,Gly(ol)5]enkephalin (DAMGO), [3H][D-Pen2,D-Pen5]enkephalin (DPDPE), [3H] (+)-(5 alpha, 7 alpha, 8 beta)-N-methyl-N-[7-(1-pyrrolidinyl) l-oxaspiro-(4,5)dec-8-yl]benzeneacetamide (U69,593), with Ki values of 3.3 +/- 0.7, 22.8 +/- 1.5 and 1.9 +/- 0.3 nM, respectively In CHO cells expressing the mu-, delta- and kappa-opioid receptors, KT-90 inhibited forskolin (10 microM)-induced cyclic AMP accumulation in a concentration-dependent manner with IC50 values of 2337 +/- 750, 17.3 +/- 4.6 and 2.0 +/- 0.1 nM, respectively. The maximal inhibitory effects of KT-90 in the cells expressing mu-, delta- and kappa-opioid receptors were significantly lower than those of the type-selective agonists DAMGO, DPDPE and U69,593, respectively. These results indicated that KT-90 acts as a partial agonist on mu-, delta- and kappa-opioid receptors. KT-90 (10 and 100 nM), when added with morphine, produced a rightward shift of the concentration-response curve of morphine to inhibit the cyclic AMP accumulation in CHO cells expressing mu-, but not delta- or kappa-, opioid receptors. This finding is consistent with the findings that lower doses of KT-90 antagonize morphine analgesia in vivo.
Katsumata
S
S
Department of Pharmacology, Faculty of Pharmaceutical Sciences, Kyoto University, Japan.
Ienaga
Y
Y
Minami
M
M
Nakagawa
T
T
Kanematsu
K
K
Satoh
M
M
D000818:Animals; D016466:CHO Cells; D002462:Cell Membrane / Q000378:metabolism; D005576:Colforsin / Q000494:pharmacology; D006224:Cricetinae; D018076:DNA, Complementary; D009020:Morphine / Q000037:antagonists & inhibitors; D009022:Morphine Derivatives / Q000378:metabolism / Q000494:pharmacology*; D011485:Protein Binding; D051381:Rats; D011957:Receptors, Opioid / Q000819:agonists* / Q000378:metabolism; D011994:Recombinant Proteins / Q000819:agonists / Q000378:metabolism
D018076:DNA, Complementary; D009022:Morphine Derivatives; D011957:Receptors, Opioid; D011994:Recombinant Proteins; C065295:KT 90; D005576:Colforsin; D009020:Morphine