Interaction of dynorphin with kappa opioid receptors in bovine adrenal medulla.
Dynorphin (Dyn) and various prototypic kappa opioid ligands were tested for their ability to bind to opioid receptors in a membrane preparation of bovine adrenal medulla and to modulate the release of catecholamines (CA) from isolated adrenal chromaffin cells. Saturation binding studies with [3H]-ethylketocyclazocine ([3H]-EKC) were performed at 37 degrees C for 30 min in the presence of [D-Ala2,Me-Phe4,Gly-ol5]-enkephalin (DAGO) and [D-Ser2,Thr6]-Leu-enkephalin (DSLET), two specific ligands for crossreacting mu and delta opioid receptors, respectively. Scatchard plot analysis of the data revealed the presence of two receptor sites: a high affinity binding site (kappa) with a KD of 0.66 nM and a Bmax of 12 pmoles/g protein and a low affinity binding site (kappa 2) with a KD of 11.1 nM and a Bmax of 56 pmoles/g protein. The presence of kappa opioid receptors in the membrane preparation was also supported by competition studies. U-50, 488H and Dyn-(1-13), two selective kappa opioid ligands, were potent inhibitors of [3H]-EKC binding with Ki (high affinity binding sites) of 2.5 and 2.3 nM, respectively. Among the various ligands tested for each class of opioid receptors (mu, delta, kappa), U-50, 488H and Dyn-(1-13) were the most potent inhibitors of the acetylcholine-evoked CA secretions from isolated adrenal chromaffin cells with IC50 of 0.31 and 1.14 microM, respectively. The inhibitory effect of U-50, 488H was significantly antagonized by diprenorphine and MR-2266, two opioid antagonists with a high affinity for the kappa opioid receptor.(ABSTRACT TRUNCATED AT 250 WORDS)
Dumont
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M
Lemaire
S
S
D000109:Acetylcholine / Q000494:pharmacology; D000313:Adrenal Medulla / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D001667:Binding, Competitive; D002395:Catecholamines / Q000378:metabolism; D002417:Cattle; D004399:Dynorphins / Q000378:metabolism*; D066298:In Vitro Techniques; D007700:Kinetics; D011957:Receptors, Opioid / Q000378:metabolism*; D017473:Receptors, Opioid, kappa
D002395:Catecholamines; D011957:Receptors, Opioid; D017473:Receptors, Opioid, kappa; D004399:Dynorphins; D000109:Acetylcholine