Functional selectivity of GPCR‐directed drug action through location bias

G protein‐coupled receptors (GPCRs) are increasingly recognized to function at intracellular membranes as well as the plasma membrane. We showed previously that the β 2 ‐adrenergic GPCR promotes cyclic AMP (cAMP) signal generation by activating the heterotrimeric G protein, G s , both from the plasma membrane and after ligand‐induced delivery of receptors to endosomes. We show here that the homologous β 1 ‐adrenergic receptor mediates a second phase of intracellular G s ‐cAMP signaling from the Golgi apparatus rather than endosomes. The Golgi‐derived activation mechanism utilizes a pre‐existing receptor pool, contrasting with endosome‐localized activation that utilizes receptors internalized from the plasma membrane, thereby requiring ligands to access the Golgi‐localized pool separately from receptors. We show that epinephrine, a hydrophilic endogenous ligand, activates the Golgi‐localized receptor pool after facilitated transport requiring extraneuronal monoamine transporter (EMT/OCT3), conferring Golgi‐localized activation that is selectively inhibited by corticosterone. We also show that clinically relevant drugs differentially access the Golgi receptor pool according to hydrophobicity, presumably through passive diffusion across membranes, and that β‐blocker drugs presently used in the clinic differ significantly in their ability to inhibit Golgi relative to plasma membrane‐localized receptor activation. These results fundamentally expand the present understanding of intracellular GPCR activation, and reveal a remarkable distinction in the cellular signaling properties of closely homologous adrenoceptor subtypes based on location. We propose the principle of ‘location bias’ as a discrete cellular scheme for discriminating the signaling properties of related GPCRs when activated by endogenous ligands, and to impose functional selectivity on receptor‐mediated drug action. Support or Funding Information K99HL122508