TABLE 1

Relative percent increase in surface μ-opioid receptor in HEK293 cells expressing the C-2 or i3-1 mutants after agonist or antagonist treatment

HEK293 cells stably expressing the C-2 or the i3-1 mutants of the μ-opioid receptor were treated with 1 μM of various opioid agonists and antagonists for 48 h. Afterward, the amount of the receptor expressed on the cell surface was determined by FACS analyses as described under Materials and Methods. The amount of receptor expressed on the cell surface after drug treatment was compared with that expressed in cells cultured in the absence of opioid ligands. The values represent the average ± S.D. of FACS analyses from cells cultured in three different plates.

i3-1 C-2
Nonselective Hydrophobic Antagonists
    (-)-Naloxone 460±84 642±18
    Naltrindole 430±6 760±25
    Naltrexone 480±1 770±63
    Diprenorphine 430±2 800±18
    Partial Agonists
    Buprenorphine 450±8 750±9
    Nalorphine 400±13 590±35
Nonselective Hydrophobic Agonists
    Etorphine 320±2 410±32
    Morphine 210±6 340±64
    Oxymorphone 290 + 2 470±28
    Levorphanol 200 + 0 340±31
    l-Methadone 240 + 0 410±24
Inactive Isomers
    (+)-Naloxone 113±19 106±5
    d-Methadone 100±0 140±8
μ-Selective Peptide Agonists
    DAMGO 97±6 98±35
    Tyr-Pro-Trp-Phe-NH2 120±1 120±16
    Tyr-Pro-Phe-Phe-NH2 95±0 110±10
μ-Selective Peptide Antagonists
    CTOP 130±2 100±7
κ-Selective Agonists
    U50-488H 120±0 120±7
    Pentazocine 97±2 120±5
κ-Selective Antagonists
    nor-Binaltorphimine 130±4 130±7