Fig. 9. Proposed model for RAMP regulation of CaSR trafficking. (A) In the absence of RAMPs (COS7 cells), the CaSR is retained (stop sign) in the endoplasmic reticulum (calnexin-positive compartment) in its incompletely processed, core-glycosylated form. (B) By contrast, in cells expressing RAMP endogenously (such as HEK293 cells), or exogenously (such as RAMP-transfected COS7 cells), the CaSR in association with RAMP1 or RAMP3 bypasses the ER retention and reaches the Golgi apparatus (giantin-positive compartment) where it is terminally glycosylated before being delivered to the cell surface.