Agonist | Ki5-a | EC505-a | Emax5-a | Relative Efficacy | Efficacy Ratio |
---|---|---|---|---|---|
nM | % | ||||
Del-II | 42.7 ± 9.7 | 9.3 ± 4.2 | 96 ± 2 | 2.80 | 1.00 |
DPDPE | 85.5 ± 7.2 | 19.1 ± 7.2 | 82 ± 2 | 2.74 | 0.98 |
SNC80 | 59.3 ± 10.2 | 15.7 ± 6.8 | 100 ± 0 | 2.39 | 0.85 |
(−)-TAN67 | 3.2 ± 0.3 | 1.4 ± 1.2 | 83 ± 5 | 1.64 | 0.59 |
Biphalin | 46.5 ± 1.5 | 34.0 ± 13.1 | 98 ± 10 | 1.18 | 0.42 |
The K i values were determined from [3H]naltrindole competitive inhibition experiments using the equation of Cheng and Prusoff (1973), and the EC50 values were determined from the [35S]GTPγS stimulation experiments as previously determined (Quock et al., 1997). Relative efficacy was determined according to Eq. 11 [0.5 ×E max/E max-sys × (1 +K D/EC50) = e rel] with E max/E max-sys = 1 as differences between the E max values for these drugs did not reach statistical significance. The K i and EC50 values for each drug were compared for statistical significance with use of a t test. These values were significantly different for Del-II, DPDPE, and SNC80 but not for (−)-TAN67 and biphalin. Hence, the relative efficacy values calculated for these latter two drugs are not significantly different than 1, the value expected for a full agonist in the absence of spare receptors.
↵5-a Values are mean ± S.E.