Impedance measurement: A new method to detect ligand-biased receptor signaling

► Niacin and synthetic analogues activate dual signaling pathways via GPR109A. ► Biased ligands of GPR109A distinguish between β-arrestin and G-protein pathways. ► Ligand-biased receptor signaling is detected by impedance measurement. Ligand-biased receptor signaling has been proposed for several G-protein coupled receptors including the niacin receptor GPR109A. Coupling to the G i/o pathway has been shown to be responsible for the well described triglyceride lowering effect of nicotinic acid in mice, while activation of the β-arrestin pathway has been suggested to be responsible for its peripheral vasodilatory effect that causes cutaneous flushing. Several ligands have been described to selectively induce triglyceride lowering without inducing flushing. Cellular impedance has been demonstrated to determine G-protein coupled receptors activation in a G-protein specific manner. Agonists, which induce triglyceride lowering, but not flushing show a profile in cellular impedance that is distinct from the one induced by niacin and those compounds that induce triglyceride lowering as well as flushing. The strength of the signal correlates with the activation of β-arrestin.