title: Capsaicin induces NKCC1 internalization and inhibits chloride secretion in colonic epithelial cells independently of TRPV1.
abstract: Colonic chloride secretion is regulated via the neurohormonal and immune systems. Exogenous chemicals (e.g., butyrate, propionate) can affect chloride secretion. Capsaicin, the pungent ingredient of the chili peppers, exerts various effects on gastrointestinal function. Capsaicin is known to activate the transient receptor potential vanilloid type 1 (TRPV1), expressed in the mesenteric nervous system. Recent studies have also demonstrated its presence in epithelial cells but its role remains uncertain. Because capsaicin has been reported to inhibit colonic chloride secretion, we tested whether this effect of capsaicin could occur by direct action on epithelial cells. In mouse colon and model T84 human colonic epithelial cells, we found that capsaicin inhibited forskolin-dependent short-circuit current (FSK-I(sc)). Using PCR and Western blot, we demonstrated the presence of TRPV1 in colonic epithelial cells. In T84 cells, TRPV1 localized at the basolateral membrane and in vesicular compartments. In permeabilized monolayers, capsaicin activated apical chloride conductance, had no effect on basolateral potassium conductance, but induced NKCC1 internalization demonstrated by immunocytochemistry and basolateral surface biotinylation. AMG-9810, a potent inhibitor of TRPV1, did not prevent the inhibition of the FSK-I(sc) by capsaicin. Neither resiniferatoxin nor N-oleoyldopamine, two selective agonists of TRPV1, blocked the FSK-I(sc). Conversely capsaicin, resiniferatoxin, and N-oleoyldopamine raised intracellular calcium ([Ca(2+)](i)) in T84 cells and AMG-9810 blocked the rise in [Ca(2+)](i) induced by capsaicin and resiniferatoxin suggesting the presence of a functional TRPV1 channel. We conclude that capsaicin inhibits chloride secretion in part by causing NKCC1 internalization, but by a mechanism that appears to be independent of TRPV1.
authors.affiliation: Department of Surgery, The University of Chicago, Chicago, IL 60637, USA. pbouyer@uchicago.edu
authors.forename: Patrice G
authors.initials: PG
authors.lastname: Bouyer
authors.forename: Xu
authors.initials: X
authors.lastname: Tang
authors.forename: Christopher R
authors.initials: CR
authors.lastname: Weber
authors.forename: Le
authors.initials: L
authors.lastname: Shen
authors.forename: Jerrold R
authors.initials: JR
authors.lastname: Turner
authors.forename: Jeffrey B
authors.initials: JB
authors.lastname: Matthews
mesh_terms: D000178:Acrylamides / Q000494:pharmacology; D000818:Animals; D019921:Biotinylation; D015153:Blotting, Western; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002211:Capsaicin / Q000494:pharmacology*; D002460:Cell Line; D002712:Chlorides / Q000378:metabolism*; D005576:Colforsin / Q000494:pharmacology; D003106:Colon / Q000187:drug effects* / Q000378:metabolism; D004224:Diterpenes / Q000494:pharmacology; D004298:Dopamine / Q000031:analogs & derivatives / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004553:Electric Conductivity; D004847:Epithelial Cells / Q000187:drug effects* / Q000378:metabolism; D006801:Humans; D007150:Immunohistochemistry; D007413:Intestinal Mucosa / Q000187:drug effects* / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D020133:Reverse Transcriptase Polymerase Chain Reaction; D028021:Sodium-Potassium-Chloride Symporters / Q000378:metabolism*; D064506:Solute Carrier Family 12, Member 2; D050916:TRPV Cation Channels / Q000235:genetics / Q000378:metabolism*; D013997:Time Factors
chemical_list: C500530:3-(4-t-butylphenyl)-N-(2,3-dihydrobenzo(b)(1,4)dioxin-6-yl)acrylamide; D000178:Acrylamides; D019086:Bridged Bicyclo Compounds, Heterocyclic; D002712:Chlorides; D004224:Diterpenes; C578877:SLC12A2 protein, human; C578878:Slc12a2 protein, mouse; D028021:Sodium-Potassium-Chloride Symporters; D064506:Solute Carrier Family 12, Member 2; D050916:TRPV Cation Channels; C494482:TRPV1 protein, human; C493921:TRPV1 protein, mouse; D005576:Colforsin; C024353:resiniferatoxin; D002211:Capsaicin; D002118:Calcium; C488796:N-oleoyldopamine; D004298:Dopamine