PCPs are further characterized by their expression of orphan GPCRs for unknown or unproven ligands. Each PCP can be distinguished from all other by specific expression of at least 2 orphan GPCRs (Figure 4M). In particular, the metabotropic Zn2+ sensor GPR39/mZnR is specifically expressed in VIP/CCK and to a less extent SST/NOS1 cells. Upon Zn2+ binding, GPR39 promotes KCC2 membrane trafficking, thereby enhancing GABAAR mediated hyperpolarization (Chorin et al., 2011). Thus GPR39 in VIP/CCK cell might mediate activity-dependent modulation of their excitability.
