G protein signaling-biased agonism at the κ-opioid receptor is maintained in striatal neurons.

Biased agonists of G protein-coupled receptors may present a means to refine receptor signaling in a way that separates side effects from therapeutic properties. Several studies have shown that agonists that activate the κ-opioid receptor (KOR) in a manner that favors G protein coupling over β-arrestin2 recruitment in cell culture may represent a means to treat pain and itch while avoiding sedation and dysphoria. Although it is attractive to speculate that the bias between G protein signaling and β-arrestin2 recruitment is the reason for these divergent behaviors, little evidence has emerged to show that these signaling pathways diverge in the neuronal environment. We further explored the influence of cellular context on biased agonism at KOR ligand-directed signaling toward G protein pathways over β-arrestin-dependent pathways and found that this bias persists in striatal neurons. These findings advance our understanding of how a G protein-biased agonist signal differs between cell lines and primary neurons, demonstrate that measuring [(35)S]GTPγS binding and the regulation of adenylyl cyclase activity are not necessarily orthogonal assays in cell lines, and emphasize the contributions of the environment to assessing biased agonism.