Somatostatin exerts multiple effects by activating distinct G protein-coupled receptors.
Here we report the cellular sites of expression of the somatostatin subtype 2A (sst 2A ) receptor in the rat enteric nervous system by using a C-terminus-specific, affinity-purified antiserum and immunohistochemistry. Antibody specificity was confirmed by the cell surface staining of human embryonic kidney 293 cells expressing the sst 2A receptor, the lack of staining of cells expressing the somatostatin subtype 2B receptor, and the abolition of staining by preincubating the antiserum with the C-terminus peptide used for immunization, sst 2A(361-369) . The sst 2A receptor antibody recognized a broad 80 kDa band on Western blots of membranes prepared from cells transfected with sst 2A receptor cDNA; following receptor membrane deglycosylation, the antibody detected an additional 40 kDa band. In the enteric nervous system, the sst 2A antibody primarily stained neurons of the myenteric and submucosal plexuses, and abundant fibers distributed to the muscle, mucosa, and vasculature. Immunoreactive staining was also observed in non-neuronal cells, including presumed interstitial cells of Cajal of the intestine and enterochromaffin-like cells of the stomach. Fibers expressing sst 2A receptor immunoreactivity were often in close proximity to D cells of the gastric and intestinal mucosa. Colocalization of somatostatin and sst 2A receptor immunoreactivities was not observed in endocrine cells nor in enteric neurons. Double-label immunohistochemistry revealed colocalization of sst 2A and vasoactive intestinal peptide immunoreactivities in enteric neurons. The multiple types of cells expressing the sst 2A receptor, including enteric neurons and nonneuronal structures, in addition to the relationship between somatostatin and sst 2A receptor elements, provide evidence that the sst 2A receptor mediates somatostatin effects in the gastrointestinal tract via neuronal and paracrine pathways.