Figure 1. SNC80-induced concentration-dependent stimulation of intracellular calcium mobilization in CHO-K1/OPRD1/Gα15 cells. The cells were loaded with Calcium-4 prior to being stimulated with agonist SNC80. The intracellular calcium change was measured by FLIPR^TETRA. The relative fluorescent units (RFU) were normalized and plotted against the log of the cumulative doses of SNC80 (Mean ± SD, n = 2). The EC₅₀ of SNC80 on this cell was 0.75 µM.
Notes:
1. EC₅₀ value is calculated with four parameter logistic equation:
Y=Bottom + (Top-Bottom)/(1+10^((LogEC₅₀-X)*HillSlope))
X is the logarithm of concentration. Y is the response
Y is RFU and starts at Bottom and goes to Top with a sigmoid shape.
2. Signal to background Ratio (S/B) = Top/Bottom

Figure 2. 5 μg of membranes prepared from CHO-K1 cells stably expressing OPRD1 receptors were incubated with indicated concentrations of [³H]Naltrindole in the absence (total binding) or presence of 1000-fold excess unlabeled Naloxone (nonspecific binding, NSB). Binding was terminated by rapid filtration. Specific binding was defined by subtracting NSB from total binding. Data were fit to one-site binding equation using a non-linear regression method.

Figure 3. 5 μg of membranes prepared from CHO-K1 cells stably expressing OPRD1 receptors were incubated with indicated concentrations of Naloxone in the presence of 0.4 nM [³H]Naltrindole. Binding was terminated by rapid filtration. Data were fit to one-site competition equation using a non-linear regression method.