SSTR2 recycling is enhanced in response to physiological signals. (A) AtT20 cells were treated for 60 min with [D-Trp⁸]-SOM to induce maximal SSTR2 internalization followed by brief acid wash and incubation in ligand-free media for 1 h at 37°C without or with 100 nM CRF, 50 nM Bay K8644, a Ca²⁺ channel agonist, or 10 µM forskolin/1 mM IBMX. Following the treatments, cells were fixed and processed for immunofluorescence with antibody recognizing SSTR2. Scale bar represents 10 µm. (B) Quantification of SSTR2 cell surface immunofluorescence intensity of three successive experiments as in A. Data were analyzed by one-factor ANOVA and Tukey comparison test (procedures implemented in GraphPad statistical package). Data are presented as least-square means ± SEMs with treatment effects significant at 0.05. (C) AtT20 cells were treated for 60 min with [D-Trp⁸]-SOM with or without 10 µM PKI followed by brief acid wash and incubation in ligand-free media for 1 h at 37°C without or with 100 nM CRF and PKI. Following the treatments, cells were fixed and processed for immunofluorescence with antibody recognizing SSTR2. Scale bar represents 10 µm. (D) Quantification of SSTR2 cell surface immunofluorescence intensity of two successive experiments as in C. Data were analyzed by one-factor ANOVA and Tukey comparison test (procedures implemented in GraphPad statistical package). **, P ≤ 0.01; ***, P ≤ 0.001. (E) Cartoon model for the induced SSTR2 recycling from the GLSV compartment. Following internalization after SOM binding, SSTR2 is sequestered in a GLUT4 like storage vesicles in endocrine cells. The recycling dynamics is very slow and can be stimulated by activation of CRF receptor (CRFR) or activation of its downstream signaling pathways.