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The effects of somatostatin (SRIF) are mediated through the seven transmembrane receptor family that signals via Gi/Go. To date, five distinct SRIF receptors have been characterized and designated SSTR1-5. We have characterized the SRIF receptor that mediates the increase in [Ca2+]i and insulin secretion in HIT-T15 cells (Simian virus 40-transformed Syrian hamster islets) using high affinity, subtype selective agonists for SSTR1 (L-797,591), SSTR2 (L-779,976), SSTR3 (L-796,778), SSTR4 (L-803,087), SSTR5 (L-817,818) and PRL-2903, a specific SSTR2 antagonist. In the presence of arginine vasopressin (AVP), SRIF increased [Ca2+]i and insulin secretion. Treatment with the SSTR2 agonist L-779,976 resulted in similar responses to SRIF. In addition, L-779,976 increased both [Ca2+]i and insulin secretion in a dose-dependent manner. Treatment with L-779,976 alone did not alter [Ca2+]i or basal insulin secretion. In the presence of AVP, all other SRIF receptor agonists failed to increase [Ca2+]i and insulin secretion. The effects of SRIF and L-779,976 were abolished by the SSTR2 antagonist PRL-2903. Our results suggest that the mechanism underlying SRIF-induced insulin secretion in HIT-T15 cells be mediated through the SSTR2. [Copyright &y& Elsevier]