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RECEPTORS AND SIGNAL TRANSDUCTION

Bitter stimuli induce Ca²⁺ signaling and CCK release in enteroendocrine STC-1 cells: role of L-type voltage-sensitive Ca²⁺ channels

Division of Digestive Diseases, Department of Medicine, CURE: Digestive Diseases Research Center and Molecular Biology Institute, David Geffen School of Medicine, University of California at Los Angeles

Submitted 5 January 2006 ; accepted in final form 9 May 2006

We previously demonstrated the expression of bitter taste receptors of the type 2 family (T2R) and the -subunits of the G protein gustducin (G_gust) in the rodent gastrointestinal (GI) tract and in GI endocrine cells. In this study, we characterized mechanisms of Ca²⁺ fluxes induced by two distinct T2R ligands: denatonium benzoate (DB) and phenylthiocarbamide (PTC), in mouse enteroendocrine cell line STC-1. Both DB and PTC induced a marked increase in intracellular [Ca²⁺] ([Ca²⁺]_i) in a dose- and time-dependent manner. Chelating extracellular Ca²⁺ with EGTA blocked the increase in [Ca²⁺]_i induced by either DB or PTC but, in contrast, did not prevent the effect induced by bombesin. Thapsigargin blocked the transient increase in [Ca²⁺]_i induced by bombesin, but did not attenuate the [Ca²⁺]_i increase elicited by DB or PTC. These results indicate that Ca²⁺ influx mediates the increase in [Ca²⁺]_i induced by DB and PTC in STC-1 cells. Preincubation with the L-type voltage-sensitive Ca²⁺ channel (L-type VSCC) blockers nitrendipine or diltiazem for 30 min inhibited the increase in [Ca²⁺]_i elicited by DB or PTC. Furthermore, exposure to the L-type VSCCs opener BAY K 8644 potentiated the increase in [Ca²⁺]_i induced by DB and PTC. Stimulation with DB also induced a marked increase in the release of cholecystokinin from STC-1 cells, an effect also abrogated by prior exposure to EGTA or L-type VSCC blockers. Collectively, our results demonstrate that bitter tastants increase [Ca²⁺]_i and cholecystokinin release through Ca²⁺ influx mediated by the opening of L-type VSCCs in enteroendocrine STC-1 cells.

type 2 family taste receptors; gastrointestinal peptides; phospholipase C ₂; Ca²⁺ fluxes; enteroendocrine cells; cholecystokinin secretion

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