Figure 3.

14-methoxycodeine-6-O-sulfate (14-OMeC6SU) compared to codeine-6-O-sulfate (C6SU) and codeine in [³⁵S]GTPγS binding assays performed in rat (A) and guinea pig (B) brain and rat spinal cord (C) membrane homogenates. For comparison standard µ-, δ- and κ-opioid receptor selective agonists, DAMGO, deltorphin II (Delt II) and U-69593, respectively are also presented. Figures represent the specific binding of [³⁵S]GTPγS in percentage (means ± S.E.M.) in the presence of increasing concentrations (0.1 nM–100 µM) of the indicated ligands. “Total” on the x-axis indicates the basal activity of the monitored G-protein (defined as 100%, its level is presented as a dotted line), which is measured in the absence of the compounds and also represents the total specific binding of [³⁵S]GTPγS. E_max and EC₅₀ ± S.E.M. values are presented in Table 2.