Regulation of carbachol-induced c-fos mRNA expression in AR42J cells by somatostatin receptor subtypes 1, 2, and 3

Introduction: Somatostatin is an inhibitory peptide that exerts its effects tissue-spccifically by activating one or more of five receptors (SSTR 1-5). Although several studies have examined which SSTR subtypes control gastrointestinal function, effects of somatostatin on pancreatic gene expression are not well defined. Aim: To examine the effects of somatostatin and newly synthesized selective SSTR agonists on the cholinergically stimulated expression of the immediate early response gene c-fos. Methodology and Results: In pancreatic acinar AR42J cells, polymerase chain reaction analysis revealed that mRNAs for SSTR 1, 2, and 3 were expressed. SSTR 4 and 5 were not detected, When AR42J cells were exposed to the cholinergic agonist carbachol in the presence of somatostatin or selective SSTR agonists, significant and dose-dependent reductions in agonist-induced levels of c-fos mRNA were noted. Pretreatment with agonists specific for SSTR 4 or 5 had no inhibitory effects. The inhibitory actions of somatostatin were pertussis toxin-sensitive. In addition, since somatostatin did not affect intracellular calcium homeostasis, the inhibitory actions of somatostatin are independent of calcium signaling. Conclusion: The current studies demonstrate that somatostatin inhibits carbachol-induced increases in c-fos expression by interacting with somatostatin receptor subtypes 1, 2, and 3. In addition, because somatostatin did not affect intracellular calcium homeostasis, it can be concluded that SSTR actions are independent of carbachol-stimulated calcium signaling.