Calcium‐sensing receptor mediates phenylalanine‐induced cholecystokinin secretion in enteroendocrine STC‐1 cells

Abstract

Intraluminal l‐phenylalanine (Phe) stimulates cholecystokinin (CCK) secretion in vivo and in vitro. However, the cellular mechanism by which CCK‐producing enteroendocrine cells sense Phe is unknown. The calcium‐sensing receptor (CaR) can sense amino acids, and is expressed in the gastrointestinal tract. In the present study, we examined whether CaR functions as a receptor for Phe in CCK‐producing enteroendocrine cells. CCK secretion and intracellular Ca2+ concentration in response to Phe were measured in the murine CCK‐producing enteroendocrine cell line STC‐1 at various extracellular Ca2+ concentrations or after treatment with a CaR antagonist. At more than 20 mm, Phe induced dose‐dependent CCK secretion and intracellular Ca2+ mobilization in STC‐1 cells. In the presence of 3.0 mm extracellular Ca2+, 10 and 20 mm Phe induced significantly higher CCK secretion than under normal conditions (1.2 mm extracellular Ca2+). Intracellular Ca2+ mobilization, induced by 10 or 20 mm Phe, was also enhanced by increasing extracellular Ca2+ concentrations. In addition, intracellular Ca2+ mobilization induced by addition of extracellular Ca2+ was augmented by the presence of Phe. These results closely match the known CaR properties. Treatment with a specific CaR antagonist (NPS2143) completely inhibited Phe‐induced CCK secretion and the latter phase of intracellular Ca2+ mobilization. CaR mRNA expression was demonstrated by RT‐PCR in STC‐1 cells, as well as in other mouse tissues including the kidney, thyroid, stomach and intestine. In conclusion, CaR functions as a receptor for Phe, stimulating CCK secretion in enteroendocrine STC‐1 cells.

The extracellular calcium-sensing receptor is required for cholecystokinin secretion in response to l-phenylalanine in acutely isolated intestinal I cells

“…CaSR transcript is also evident in the STC-1 cell line (16), suggesting that CaSR expression is specific to neuroendocrine cells. Conflicting evidence localizing CaSR protein throughout the basilar aspect of absorptive duodenal epithelial cells exists (7).…”

“…In a recent STC-1 cell study, phenylalanine-induced mobilization of intracellular calcium and CCK secretion was inhibited with the allosteric CaSR inhibitor NPS2143 (16), further supporting a putative role for the CaSR in CCK secretion. However, it is unknown whether this receptor is functionally expressed by the native intestinal I cell, and whether it functions to regulate L-amino acid-induced CCK secretion as a nutrient sensor.…”

Calcium-sensing receptor is a physiologic multimodal chemosensor regulating gastric G-cell growth and gastrin secretion

“…2 C and D). These results provide a molecular basis for protein meal stimulation of gastrin and by logical extension, may account for amino acid stimulation of other CaR-expressing cells, such as acid-secreting parietal cells (17), cholecystokinin-secreting enteroendocrine I cells (28), and insulin-secreting β cells (29).…”

“…This acid stimulatory effect of cinacalcet acting on both the G (42) and parietal cell (18) may warrant acid suppressive therapy to prevent cinacalcet intolerance caused by hyperacidity in vulnerable hemodialysis patients on long-term therapy for secondary hyperparathyroidism (43). The inhibition of gastrin secretion by NPS 2143 suggests that clinical trials of calcilytics for the treatment of osteoporosis should monitor potential deleterious inhibition of CaR on nonclassical Ca 2+ regulatory tissues (9,27,28).…”

Sensing of amino acids by the gut-expressed taste receptor T1R1-T1R3 stimulates CCK secretion

“…Phe, Leu, and Glu stimulation of T1R1-T1R3 is enhanced in the presence of IMP, while Trp does not activate this receptor (49). Phe, Leu, and Trp are also known to evoke CCK release (2,26,61). We also assessed the effect of D-isomers of these amino acids to show potential specificity.…”