Affinity (Ki) values and inhibition of adenylyl cyclase activity by morphine and DPDPE in opioid naı̈ve GH3DORT8 cells and in cells chronically treated with morphine or DPDPE
| Acute Drug | Chronic Pretreatment | BindingKi | Adenylyl Cyclase | |
|---|---|---|---|---|
| IC50 | Imax | |||
| nM | nM | % | ||
| Morphine | None | 116.8 ± 15.41-160 | 272.1 ± 21.31-160 | 72.7 ± 0.67 |
| DPDPE | None | 6.08 ± 1.11-152 | 0.43 ± 0.041-c | 71.3 ± 1.21-c |
| DPDPE | Morphine | N.T. | 1.69 ± 0.131-c | 73.3 ± 1.71-c |
| DPDPE | DPDPE | N.T. | 11.3 ± 3.21-a 1-b | 59.3 ± 1.91-a 1-b |
The affinity of morphine or DPDPE for δ-opioid receptors in GH3DORT8 cell membranes was determined by their displacement of 1 nM [3H]diprenorphine. Affinity (Ki) values are expressed as mean ± S.E.M and were calculated from IC50 values derived from complete concentration-effect curves. The Kd for diprenorphine used to calculate theKi values in membranes was obtained fromMartin et al. (2002) and is 0.71 ± 0.04 nM. The ability of δ-opioid agonists to reduce 10 μM forskolin-stimulated cAMP accumulation was assessed in whole GH3DORT8 cells, as described under Materials and Methods. The IC50 andImax values for each drug were determined by nonlinear regression analysis. Representative concentration-effect curves and control values are provided in Fig. 2. Data presented represent the mean ± S.E.M. for three experiments performed in triplicate.
N.T., not tested.
↵1-160 Significantly different from corresponding (Acute) DPDPE/(Chronic) None value (P < 0.01; Student'st test).
↵1-152 Values obtained from Martin et al. (2001).
↵1-a Significantly different from corresponding (Acute) DPDPE/(Chronic) None value (P < 0.05; one-way ANOVA plus Tukey's post hoc test).
↵1-b Significantly different from corresponding (Acute) DPDPE/(Chronic) Morphine value (P< 0.05; one-way ANOVA plus Tukey's post hoc test).
↵1-c Significantly different from corresponding (Acute) DPDPE/(Chronic) DPDPE value (P < 0.05; one-way ANOVA plus Tukey's post hoc test).