Demonstration of the heterogeneity of the kappa-opioid receptors in guinea-pig cerebellum using selective and nonselective drugs.
In guinea-pig cerebellum, saturation studies reveal that the nonselective opioid [3H]ethylketazocine has a binding capacity (R) of 6.79 pmol/g tissue which is similar to the sum of the individual R values of the mu-, delta- and kappa 1-selective opioids. Conversely, the binding parameters of the nonselective opioid [3H]bremazocine are best-fitted to a two-site model (Kd1 = 0.12 nM, R1 = 11.3 pmol/g tissue; Kd2 = 6.03 nM, R2 = 9.09 pmol/g tissue) with an R TOTAL value of 20.3 pmol/g tissue which is statistically different from the R value of [3H]ethylketazocine or the sum of R mu + R delta + R kappa 1. This suggests that [3H]bremazocine labels additional opioid binding sites. After suppression of the mu-, delta- and kappa 1-receptors, [3H]bremazocine binding is then best-fitted to a one-site model with a Kd value of 1.48 nM and an R value of 11.2 pmol/g tissue. Competition studies done against the binding of [3H]U69593 indicate that the opioid receptors labelled with this ligand are related to the kappa 1-receptor subtype. However, competition studies performed against the binding of [3H]bremazocine (under suppressed conditions) display a pharmacological profile related to another subtype of kappa-receptors previously described in guinea-pig brain as the kappa 2-receptors.
Tiberi
M
M
Département de pharmacologie, Université de Montréal, Quebec, Canada.
Magnan
J
J
D000818:Animals; D044482:Benzeneacetamides; D001575:Benzomorphans / Q000378:metabolism; D001667:Binding, Competitive / Q000187:drug effects; D002531:Cerebellum / Q000032:analysis* / Q000187:drug effects / Q000378:metabolism; D003201:Computers; D003496:Cyclazocine / Q000031:analogs & derivatives / Q000494:pharmacology; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D020881:Enkephalin, D-Penicillamine (2,5)-; D004745:Enkephalins / Q000378:metabolism / Q000494:pharmacology; D016314:Ethylketocyclazocine; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D008566:Membranes / Q000187:drug effects / Q000378:metabolism; D011759:Pyrrolidines / Q000494:pharmacology; D011957:Receptors, Opioid / Q000032:analysis* / Q000378:metabolism; D017465:Receptors, Opioid, delta; D017473:Receptors, Opioid, kappa; D017450:Receptors, Opioid, mu
D044482:Benzeneacetamides; D001575:Benzomorphans; D004745:Enkephalins; D011759:Pyrrolidines; D011957:Receptors, Opioid; D017465:Receptors, Opioid, delta; D017473:Receptors, Opioid, kappa; D017450:Receptors, Opioid, mu; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D016314:Ethylketocyclazocine; D020881:Enkephalin, D-Penicillamine (2,5)-; C027248:bremazocine; C045444:U 69593; D003496:Cyclazocine