Further characterization of [3H]U69593 binding sites in the rat heart.
K binding sites in the crude membrane preparation of the rat heart homogenate were further characterized by a displacement binding assay of [3H]-U69593 with specific kappa ligands and a direct binding assay with [3H]-etorphine. Scatchard analysis of specific [3H]-U69593 binding showed that the Kd and Bmax were 6.4 +/- 1.0 nM and 97 +/- 8 fmol/mg protein. respectively. The binding of [3H]-U69593 was effectively displaced by the selective kappa 1 ligands, U-69593 and U-50488H, but only weakly displaced by Met5-enkephalin-Arg6-Phe7, a selective kappa 2 ligand, which showed only 11 +/- 3% inhibition of [3H]-U69593 binding at the concentration of 1 microM. In addition, there was no binding site for [3H]-etorphine, known to bind to mu, delta and kappa 2 binding sites, but not kappa 1 binding sites. The findings suggest that the kappa binding sites in the rat heart most likely belong to the kappa 1 subtype. The binding sites have high and low affinity components as nonlinear regression analysis of the competition curves is best fit by two components with IC50 values of 11 +/- 2 and 62 +/- 7 nM for U-69593, and 9.9 +/- 1.5 and 414 +/- 108 nM for U-50488H. Furthermore, the binding of [3H]-U69593 were inhibited by both monovalent cations (Na+, Li+) and divalent cations (Mg2+, Mn2+ and Ca2+).
Department of Physiology, Faculty of Medicine, University of Hong Kong, Hong Kong.
W Q
WQ
Jin
K K
KK
Tai
T K
TK
Chan
T M
TM
Wong
D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; D000700:Analgesics / Q000378:metabolism*; D000818:Animals; D044482:Benzeneacetamides; D001665:Binding Sites; D001921:Brain / Q000378:metabolism; D005048:Etorphine / Q000378:metabolism; D005260:Female; D007700:Kinetics; D009206:Myocardium / Q000378:metabolism*; D009928:Organ Specificity; D011759:Pyrrolidines / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017473:Receptors, Opioid, kappa / Q000819:agonists*; D014316:Tritium
D000700:Analgesics; D044482:Benzeneacetamides; D011759:Pyrrolidines; D017473:Receptors, Opioid, kappa; D014316:Tritium; D005048:Etorphine; D019900:3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; C045444:U 69593