**8. Receptor promiscuity and biased signaling**

GPCR "promiscuity" is defined as the ability of a given receptor to activate several different effectors (for review: (Hermans, 2003). While most receptors can probably induce parallel signaling by the GαGTP and Gβγ subunits (see above), some are capable of activating different G proteins; and some use both G protein dependent and G protein independent signaling pathways.

"Biased signaling" refers to the observation that when receptors two or more signaling pathways, a few agonists preferentially use only one of the signaling pathways available to the other agonists – an observation that suggests that the activated receptor takes different conformations, depending on the agonist occupying its binding site.
