Additionally, we previously found that the DAMGO and β-endorphin pharmacology were also similar in sensory neurons between 118AA and 118GG allele carriers25. These findings differed from a study that reported a 3-fold increase in potency by β-endorphin with regard to activating G protein-gated inwardly rectifying K+ channels in frog oocytes expressing 118G MOR when compared to 118A receptors1. The difference between morphine and these three other opioid receptor agonists may be due to differences in the physical binding to the receptors (see Discussion, page 14, second paragraph, 4th-6th sentences) or the signaling components (i.e. heterotrimeric G proteins) that couple each MOR subtype and effectors (i.e. ion channels and enzymes) are different or there are other differences between each model system employed (i.e. native vs. heterologous expression levels).
