Abstract

In most tissues and cells the opioid receptor-like (ORL₁) receptor regulates effectors primarily through the pertussis toxin (PTX)-sensitive guanine nucleotide-binding regulatory proteins (G proteins) G_i/G_o. Many G_i-coupled receptors possess additional capability to interact with one or more PTX-insensitive G proteins. Using the βγ-induced stimulation of type 2 adenylyl cyclase as a readout, we screened the ability of ORL₁ receptor to interact with a panel of PTX-insensitive G proteins. In the presence of PTX, activation of the ORL₁ receptor resulted in the stimulation of type 2 adenylyl cyclase only in HEK 293 cells coexpressing the α subunit of G_z, G₁₂, G₁₄, or G₁₆, but not in cells coexpressing G₁₁, G₁₃, or G_q. Coupling to both G_z and G₁₆ was expected because close relatives of the ORL₁ receptor, the opioid receptors, are known to couple productively to these G proteins. ORL₁ receptor coupling to either G₁₂ or G₁₄ has not been demonstrated. As predicted by the type 2 adenylyl cyclase assays, activation of the ORL₁ receptor resulted in the formation of inositol phosphates in COS-7 cells transiently cotransfected with Gα₁₄. The ORL₁receptor-mediated stimulation of phospholipase C was found to be Gα₁₄ dependent, agonist dose dependent, ligand selective, and PTX insensitive. We conclude that G₁₄ can link the ORL₁ receptor to regulation of phopholipase C.