Fig. 2.
Agonist-selective phosphorylation and internalization of the sst2A receptor in vivo. A, Rats were killed at 90 min after injection of octreotide (50 μg/kg) or SOM230 (50 μg/kg). Pituitary and pancreas of each animal were collected, fixed in formalin, and embedded in paraffin for immunohistochemical staining using the phosphorylation-state independent antibody UMB-1. Note that octreotide but not SOM230 stimulated a robust redistribution of sst2A receptors from the plasma membrane into the cytosol in both tissues. In contrast, SOM230 was not able to stimulate in vivo internalization of sst2A. Scale bar, 10 μm. B, Rats were killed at 30 min after injection of octreotide (50 μg/kg) or SOM230 (50 μg/kg). The pancreas of each animal was collected. The levels of phosphorylated sst2A receptors (upper panel) and total sst2A receptors (lower panel) were then determined by Western blot analysis. Note that octreotide stimulated a robust phosphorylation of sst2A receptors. In contrast, SOM230 was not able to stimulate in vivo phosphorylation of sst2A. The positions of the molecular mass markers are indicated on the left (in kilodaltons).