Table 2

Competitive inhibition of [3H]DAMGO binding by β-CNA to GH3MOR cell membranes in the presence or absence of GppNHp/NaCl. The displacement of [3H]DAMGO binding by β-CNA to membranes prepared from control and morphine or DAMGO-pretreated GH3MOR cells was assessed. Cells were treated with or without 10 μM morphine or DAMGO for 48 h. Membranes were prepared from extensively washed cells as described under Experimental Procedures. Competition binding was determined with 3 nM [3H] DAMGO and various concentrations of β-CNA in the presence or absence of 25 μM GppNHp and 100mM NaCl. Results are the mean ± S.E.M. from three or four experiments preformed in triplicate.

Chronic PretreatmentIC50IC50 (high)/IC50 (low)Ratio
−GppNHp/NaCl (High)+GppNHp/NaCl (Low)
nM
NONE3.83  ± 0.8410.20  ± 4.020.38
MORPHINE5.03  ± 0.891.57  ± 0.352-a 3.20
DAMGO4.30  ± 0.610.33  ± 0.092-b 13.03
  • 2-a  Significantly different from corresponding (high) IC50 value, p < 0.05, (unpaired Student's t test).

  • 2-b  Significantly different from corresponding (high) IC50 value, p < 0.01, (unpaired Student's t test).