Gi1 and GoA differentially determine kinetic efficacies of agonists for κ‐opioid receptor

Abstract
We examined the diversity of single receptor function by measuring receptor–G protein coupling in the baculovirus–Sf21 expression system. In comparative studies using Sf21 cell membranes expressing κ-opioid receptor (KOR) plus Gαi1β1γ2 or KOR plus GαoAβ1γ2, there was no significant difference between both preparations in the Ki values of various κ-opioid ligands for the displacement of [3H]U69593 binding. However, a marked difference in the rank order of agonists to stimulate [35S]GTPγS binding was observed between both preparations. These findings suggest that agonist efficacy is dependent on the population of different G proteins expressed in various tissues