EC50 values for morphine, etorphine, and DAMGO in intact HEK-μ cells, calculated from dose-response curves (n= 3) using the following measures: stimulation of Ca2+fluorescence (whole cells; 5–7 s and 20–22 s), and inhibition of forskolin-stimulated cAMP accumulation in HEK-μ cell suspension
| A. Stimulation of Ca2+response, EC50 (nM, ± S.D.) | |||
| 1.3 mM Extracellular Ca2+ | No Extracellular Ca2+ | ||
| 5–7 s | 20–22 s | 20–22 s | |
| Morphine | 40 ± 7 | 40 ± 16 | 37 ± 7 |
| ratio 1.0 ± 0.2 | |||
| Etorphine | 2.9 ± 0.2 | 0.14 ± 0.051-a | 1.0 ± 0.9 |
| ratio 22 ± 7 | |||
| DAMGO | 21 ± 1 | 6.7 ± 1.41-a | Not done |
| ratio 3.2 ± 0.7 | |||
| B. Inhibition of cAMP Accumulation | |||
| EC50 (nM, ± S.D.) | Slope | E max ± S.D. | |
| Morphine | 24 (±4) | 0.96 | 45 ± 2% |
| Etorphine | 1.6 (±0.9) | 1.3 | 42 ± 1% |
Slope factors for the Ca2+ responses did not deviate substantially from unity and were fixed to 1 (see Fig. 2 for fluorescence response profiles). Each experiment was replicated at least once with similar results.
↵1-a Comparing 5 to 7 s versus 20 to 22 s, p < 0.001, Student'st, two-tailed, non-matched pairs.