Many important signaling events in excitable cells are regulated by G protein coupled receptors such as α2 adrenergic receptors. These receptors are exposed to the strong electric field of the membrane. It has been previously hypothesized that activation of certain GPCRs, is affected by voltage (Ben-Chaim 2003;Ben-Chaim 2006; Martinez-Pinna 2005). The development of FRET-based assays to determine receptor activation on the level of the receptor opened the path to study effects of voltage on receptor activity directly. We employed FRET probes for α_2A-adrenergic receptors (α_2AAR), and downstream events such as receptor / G protein interaction and G protein activation and measured FRET- signals in single cells under conditions of voltage clamp. Non activated receptors did not show any voltage dependent activity. However, at negative membrane potentials norepinephrine (NE) was more potent in activating α_2A-AR in comparison to positive potentials. Similarly, negative voltages potentate agonist induced α_2A AR / G protein interactions as well as NE induced G protein activity. At intermediate concentrations of NE (10 µM) the receptor switched on and off in dependence of the membrane potential. The concentration response curve of NE-evoked α_2A AR activation was shifted 2-3 fold by application of positive potential without affecting maximal receptor activation. These results are in line with the hypothesis that binding of the charged agonist within the electrical field of the membrane represent a major mechanism for voltage dependence of GPCR activation. This concept is further supported by the notion that A_2A-adenosine receptors which bind non charged agonists did not show any voltage dependence as detected by means of a similar FRET approach. This study is the first to prove the existence of voltage dependent activation of a GPCR on the level of the receptor.