Characterization of the inhibitory effect of boiled rice on intestinal chloride secretion in guinea pig crypt cells.
OBJECTIVE
When rice is incorporated into oral rehydration therapy for patients with secretory diarrhea, clinical outcomes improve. We have shown that a factor purified from boiled rice (RF) blocks the secretory response of intestinal crypt cells to adenosine 3',5'-cyclic monophosphate (cAMP). Now we report that the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel is the cellular target for this rice inhibitor.


METHODS
We used RF, the same previously described extract prepared from boiled rice, to assess chloride channel activation in vitro, measuring (1) cell volume regulation of guinea pig intestinal crypt epithelial cell suspensions using standard Coulter counter technology, (2) transepithelial chloride current in monolayers of T84 cells mounted in Ussing chambers, and (3) whole-cell and single-channel currents using the patch-clamp technique in cells transfected to express CFTR.


RESULTS
RF inhibited activation by cAMP of CFTR chloride channels in all experimental preparations; RF did not block volume-stimulated Cl- secretion, suggesting that its effect might be specific for CFTR chloride channels. RF inhibited transepithelial cAMP-stimulated Cl- current in T84 cells and inhibited forskolin (i.e., cAMP)-induced current in cells transfected with CFTR. Excised patch and single-channel patch-clamp recordings supported the view that the response was a direct effect on CFTR rather than on cAMP signal transduction.


CONCLUSIONS
RF exerts a specific inhibitory effect on CFTR chloride channels, blocking activation from the luminal surface of the cell and reversing established activation. Many major diarrheal states are based on cAMP-induced CFTR activation, leading to excessive gut secretion; our findings could have clinical relevance.
Mathews
C J
CJ
Department of Physiology, McGill University, Montreal, Canada.
MacLeod
R J
RJ
Zheng
S X
SX
Hanrahan
J W
JW
Bennett
H P
HP
Hamilton
J R
JR
D000818:Animals; D016466:CHO Cells; D002460:Cell Line / Q000187:drug effects / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism* / Q000502:physiology; D003296:Cooking; D006224:Cricetinae; D000242:Cyclic AMP / Q000494:pharmacology; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology; D004553:Electric Conductivity; D006168:Guinea Pigs; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism*; D007422:Intestines / Q000166:cytology; D012275:Oryza / Q000737:chemistry; D018408:Patch-Clamp Techniques; D010936:Plant Extracts / Q000494:pharmacology; D014162:Transfection
C505032:CFTR protein, human; D002712:Chlorides; D010936:Plant Extracts; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D000242:Cyclic AMP