KAPPA-OPIOID BINDING-SITES ON THE R1.1 MURINE LYMPHOMA CELL-LINE - SENSITIVITY TO CATIONS AND GUANINE-NUCLEOTIDES

The present study describes the characterization of an opioid binding site on membranes prepared from the R1.1 cell line, a murine thymoma. Specific (-)[H-3]bremazocine binding was saturable, stereoselective, and limited to a single high affinity binding site with a K(d) value of 15.2 +/- 1.6 pM and a B(max) value of 54.8 +/- 6.0 fmol/mg of protein. The kappa-selective alkaloids and dynorphin peptides inhibited (-)[H-3]bremazocine binding with K(i) values of less than 1 nM, in contrast to mu- and delta-selective-ligands. The high affinity of this site for alpha-neo-endorphin and U50,488 suggests that this kappa Opioid binding site resembles the kappa1b subtype. NaCl, as well as other mono- and divalent cations, inhibited (-)[H-3]bremazocine binding. In the presence of NaCl, the nucleotides GTP, GDP, and the nonhydrolyzable analog guanylyl-5'-imidodiphosphate (Gpp(NH)p) also decreased (-)[H-3]bremazocine binding, suggesting that thiS kappa opioid binding site is coupled to a G-protein. In summary, R1.1 cells possess a single high affinity kappa opioid receptor that shares many properties with brain kappa1b opioid receptors.