Bitter stimuli induce Ca2+ signaling and CCK release in enteroendocrine STC-1 cells: role of L-type voltage-sensitive Ca2+ channels.
We previously demonstrated the expression of bitter taste receptors of the type 2 family (T2R) and the alpha-subunits of the G protein gustducin (Galpha(gust)) in the rodent gastrointestinal (GI) tract and in GI endocrine cells. In this study, we characterized mechanisms of Ca(2+) 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 [Ca(2+)] ([Ca(2+)](i)) in a dose- and time-dependent manner. Chelating extracellular Ca(2+) with EGTA blocked the increase in [Ca(2+)](i) induced by either DB or PTC but, in contrast, did not prevent the effect induced by bombesin. Thapsigargin blocked the transient increase in [Ca(2+)](i) induced by bombesin, but did not attenuate the [Ca(2+)](i) increase elicited by DB or PTC. These results indicate that Ca(2+) influx mediates the increase in [Ca(2+)](i) induced by DB and PTC in STC-1 cells. Preincubation with the L-type voltage-sensitive Ca(2+) channel (L-type VSCC) blockers nitrendipine or diltiazem for 30 min inhibited the increase in [Ca(2+)](i) elicited by DB or PTC. Furthermore, exposure to the L-type VSCCs opener BAY K 8644 potentiated the increase in [Ca(2+)](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 [Ca(2+)](i) and cholecystokinin release through Ca(2+) influx mediated by the opening of L-type VSCCs in enteroendocrine STC-1 cells.
Chen
Monica C
MC
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 90095-1786, USA.
Wu
S Vincent
SV
Reeve
Joseph R
JR
Rozengurt
Enrique
E
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000502:physiology*; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D002460:Cell Line; D002766:Cholecystokinin / Q000378:metabolism*; D019858:Enteroendocrine Cells / Q000187:drug effects / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004963:Estrenes / Q000494:pharmacology; D007425:Intracellular Membranes / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D010670:Phenylthiourea / Q000494:pharmacology; D011506:Proteins / Q000378:metabolism; D011760:Pyrrolidinones / Q000494:pharmacology; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology; D015398:Signal Transduction / Q000502:physiology; D012964:Sodium / Q000378:metabolism; D050053:TRPM Cation Channels / Q000378:metabolism; D013649:Taste / Q000502:physiology*; D013997:Time Factors; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors
D002118:Calcium; D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D002766:Cholecystokinin; D004791:Enzyme Inhibitors; D004963:Estrenes; D010670:Phenylthiourea; D011506:Proteins; D011760:Pyrrolidinones; D000644:Quaternary Ammonium Compounds; D012964:Sodium; D050053:TRPM Cation Channels; D010738:Type C Phospholipases; C476766:TRPM4 protein, mouse; C498617:Trpm5 protein, mouse; C060229:1-(6-((3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione; C043414:denatonium