Kappa opioid binding sites on the R1.1 murine lymphoma cell line: sensitivity to cations and guanine nucleotides

Abstract

The present study describes the characterization of an opioid binding site on membranes prepared from the R1.1 cell line, a murine thymoma. Specific (−)[ 3H]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 κ-selective alkaloids and dynorphin peptides inhibited (−)[ 3H]bremazocine binding with K i values of less than 1 nM, in contrast to μ- and σ-selective ligands. The high affinity of this site or α-neo-endorphin and U50,488 suggests that this κ opioid binding site resembles the κ 1 b subtype. NaCl, as well as other mono- and divalent cations, inhibited (−)[ 3H]bremazocine binding. In the presence of NaCl, the nucleotides GTP, GDP, and the nonhydrolyzable analog guanylyl-5′-imidodiphosphate (Gpp(NH)p) also decreased (−)[ 3H]bremazocine binding, suggesting that this κ opioid binding site is coupled to a G-protein. In summary, R1.1 cells posses a single high affinity κ opioid receptor that shares many properties with brain κ 1 b opioid receptors.