Fig. 5
From: Platelet P2Y1 receptor exhibits constitutive G protein signaling and β-arrestin 2 recruitment
P2Y1-R constitutive activity depends on receptor expression level. Increasing P2Y1-R expression switched the receptor equilibrium from an inactive R conformation to an active R* conformation, thereby promoting a constitutive activation of Gq protein signaling as well as constitutive recruitment of β-arrestin 2, and precluding ADP-induced signaling. By contrast, decreasing P2Y1-R expression had an opposite effect, balancing the receptor equilibrium towards an inactive R state responding to agonist stimulation