Parameters of [3H]Naloxone binding in membranes from PTX-treated, agonist-tolerant cells
| Treatment (10 μm) | [3H]Naloxone binding | |||
|---|---|---|---|---|
| Kd | Bmax | Reduction in Bmax (a) | Change3-a | |
| nm | fmol/mg | % | % | |
| Control | 1.73 ± 0.15 | 8617 (365) | ||
| DAMGO | 1.72 ± 0.17 | 4458 (68) | 48 | 83 |
| Morphine | 2.21 ± 0.21 | 7480 (190) | 13 | 22 |
| Butorphanol | 4.93 (2.28) | 8244 (248) | 4 | 7 |
| Etorphine | 5.46 (2.36) | 4623 (361) | 46 | 79 |
[3H]Naloxone binding was measured in membranes prepared from cells treated with PTX (20 ng/ml for 24 hr) followed by 10 μm agonist for an additional 12 hr. Cells treated with only PTX in the absence of any agonist constituted control for this experiment. Under these conditions, DAMGO induced down-regulation of 58% of the [3H]naloxone binding sites in cells containing functional inhibitory G protein (b; Table2). Values are mean ± standard error from three experiments. Mean and range values are given for experiments repeated in duplicate.
↵3-a Percentage of the reduction inB max in PTX-treated cells (a) divided by the reduction in B max in control cells (Table 2).