Kappa opioid binding sites in the dog cerebral cortex and spinal cord.
In the dog cerebral cortex and spinal cord, [3H]bremazocine and [3H]U69593 both bound with high affinity to an apparent single population of binding sites under kappa-selective conditions. In the cortex similar Bmax values for both radioligands in the saturation studies and the high affinity of the kappa-selective agents PD117302 and U69593 for both [3H]bremazocine and [3H]U69593 labelled sites in the competition studies suggested a predominance of U69593-sensitive sites previously described as kappa 1 in the guinea-pig and rat brain. The lower slope values for the inhibition curves of PD117302 and U69593 against [3H]bremazocine but not against [3H]U69593 suggested that [3H]bremazocine could also be binding to a relatively minor proportion of additional, possibly kappa 2, sites while [3H]U69593 would appear to be selective for the kappa 1 site. In contrast, in the dog spinal cord, [3H]U69593 appeared to recognize only a proportion (approximately 35%) of the [3H]bremazocine labelled binding site. The significantly lower affinities and slope values of U69593 and PD117302 against [3H]bremazocine were consistent with the additional sites representing the k2 (benzomorphan) sites previously described in guinea-pig and rat spinal cord. Alternatively, the low (micromolar) affinity of the mu-selective ligand, [D-Ala2, MePhe4, Gly-ol5]enkephalin, implied that these additional sites might not be kappa 2 but possibly a low affinity mu site normally expressed under more physiological conditions.
Hunter
J C
JC
Parke-Davis Research Unit, Addenbrooke's Hospital Site, Cambridge, U.K.
Birchmore
B
B
Woodruff
R
R
Hughes
J
J
D000818:Animals; D044482:Benzeneacetamides; D001575:Benzomorphans / Q000378:metabolism*; D002540:Cerebral Cortex / Q000378:metabolism*; D004285:Dogs; D009019:Morphinans / Q000378:metabolism*; D011759:Pyrrolidines / Q000378:metabolism*; D011957:Receptors, Opioid / Q000378:metabolism*; D017473:Receptors, Opioid, kappa; D013116:Spinal Cord / Q000378:metabolism*
D044482:Benzeneacetamides; D001575:Benzomorphans; D009019:Morphinans; D011759:Pyrrolidines; D011957:Receptors, Opioid; D017473:Receptors, Opioid, kappa; C027248:bremazocine; C045444:U 69593