CONTROL OF SOMATOSTATIN SECRETION BY CCK-1 AND CCK-2 RECEPTORS IN RIN-14B CELLS, A RAT PANCREATIC ISLET CELL LINE

Abstract

Background: In normal pancreatic islets of seven different species, the CCK-1 receptors were located on insulin and glucagon cells, while the CCK-2 receptors were observed on somatostatin (SS) cells. The objectives of this study were to establish the presence of the CCK receptors (CCKR) subtypes in RIN-14B cells, a SS secreting cell line and determine the implication of these receptors in SS secretion. Methods: RIN-14B cells were grown in RPMI 1640 medium. Western blot (WB) analyses were performed to detect the CCKR subtypes in cell membranes. The localization of the CCKR subtypes, insulin and SS in cells was investigated by immunofluorescence. Effects of either caerulein or pentagastrin (PG) alone or in combinaison with CCKR specific antagonists on SS secretion were evaluated by ELISA over 4 h. Results: WB analyses with specific antibodies identified both CCKR in RIN-14B cells. By immunofluorescence, both subtypes appear on SS cells (95%) and CCK-1R on insulin cells (5%). Cearulein and PG caused a conc.- dependent increase in SS secretion. Cearulein at 10−6 M caused a maximal 3-fold increase (basal 225 pg/mL ± 29) in SS release, whereas PG effect was maximal at 10−5 M with a 2.5-fold increase. Cells release 80-90% of their SS content in the culture medium. Addition of L-364,718 (anti CCK-1R)at 10−7 M and L-365,260 (anti CCK-2R) at 10−5 M, to PG (10−5 M), reduced SS release by 26% and 51%, respectively. Conclusion: CCKR subtypes are present with SS in RIN-14B pancreatic islet cells. The cells displayed high basal SS secretion significantly stimulated by caerulein and PG. This response was mostly CCK-2R dependent. Further investigations on the effect of caerulein and PG on RIN-14B cell growth are presently underway. Future data may clarify the role of CCKR subtypes in endocrine pancreatic SS cells physiology. Funded by NSERC Canada.