Table 1

Efficacy and potency of opioid agonists for stimulation of [35S]GTPγS binding to rat thalamus, SK-N-SH, and mMOR-CHO membranes

MembraneAgonistED50Maximum Stimulation
nm %
Rat thalamusDAMGO222  ± 42100  ± 5.0
Fentanyl117  ± 2158  ± 4.7
Morphine434  ± 12156  ± 3.0
Buprenorphine0.74  ± 0.4810  ± 1.5
SK-N-SH cellsDAMGO73.6  ± 8.0100  ± 8.0
Fentanyl37.5  ± 6.366  ± 6.6
Morphine138  ± 1273  ± 5.8
Buprenorphine0.14  ± 0.0415  ± 1.1
mMOR-CHO cellsDAMGO32.2  ± 5.2100  ± 4.5
Fentanyl23.0  ± 4.1110  ± 1.1
Morphine120  ± 24106  ± 3.0
Buprenorphine3.6  ± 1.243  ± 2.4
Levallorphan2.7  ± 1.212  ± 1.0

Membranes were incubated with various concentrations of opioid agonists in the presence of 0.05 nm [35S]GTPγS and 30 μm (rat thalamus and SK-N-SH) or 10 μm(mMOR-CHO) GDP. Data are mean ± standard error of ED50 (nm) and E maxvalues (percent maximal stimulation obtained with 10 μmDAMGO). Maximal stimulation over basal by DAMGO was 167 ± 8.4%, 222 ± 18%, and 414 ± 18% in rat thalamic, SK-N-SH, and mMOR-CHO cell membranes, respectively. Basal [35S]GTPγS binding was 87.6 ± 12.0, 7.8 ± 0.7, and 21.3 ± 1.3 fmol/mg of protein in rat thalamic, SK-N-SH, and mMOR-CHO cell membranes, respectively.