Antisecretory effect of loperamide in colon epithelial cells by inhibition of basolateral K+ conductance.
BACKGROUND
The mechanism of the antisecretory effect of loperamide was investigated in cultured highly differentiated colon epithelial cells (HT-29/B6).


METHODS
Chloride secretion was stimulated via cAMP by forskolin (FSK, 10(-5) M), via Ca2+ by the muscarinic agonist carbachol (CCh, 10(-4) M), and via protein kinase C by the phorbol ester PMA (5 x 10(-9) M). Stimulated Cl- secretion was quantified as short circuit current (I(SC)) of HT-29/B6 monolayers mounted in Ussing-type chambers.


RESULTS
Loperamide (5 x 10(-5) M) inhibited I(SC) stimulated by FSK, CCh and PMA. The antisecretory action of loperamide was unaffected by preincubation with naloxone (10(-5) M). Furthermore, loperamide strongly inhibited basolateral 86Rb efflux. Like loperamide, the calmodulin antagonist trifluoperazine (10(-4) M) inhibited I(SC) induced by FSK, CCh or PMA. The Ca2+ channel blocker verapamil (5 x 10(-5) M), on the other hand, inhibited only PMA-stimulated I(SC),but had no effect on FSK or CCh-induced I(SC) CONCLUSIONS: Loperamide exerts a direct antisecretory action on chloride secretion of colon epithelial cells independently of the respective stimulatory signal transduction pathway. This antisecretory effect is not mediated by opiate receptors and reflects inhibition of basolateral K+ conductance.
Epple
H J
HJ
Dept. of Gastroenterology, Universitätsklinikum Benjamin Franklin, Freie Universität Berlin, Germany.
Fromm
M
M
Riecken
E O
EO
Schulzke
J D
JD
D000930:Antidiarrheals / Q000494:pharmacology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002147:Calmodulin / Q000037:antagonists & inhibitors; D002217:Carbachol / Q000494:pharmacology; D002712:Chlorides / Q000502:physiology*; D018679:Cholinergic Agonists / Q000494:pharmacology; D005576:Colforsin / Q000494:pharmacology; D003106:Colon / Q000166:cytology*; D004353:Drug Evaluation, Preclinical; D020895:Enterocytes / Q000187:drug effects* / Q000378:metabolism*; D019073:HT29 Cells / Q000187:drug effects* / Q000378:metabolism*; D006801:Humans; D007413:Intestinal Mucosa / Q000187:drug effects* / Q000378:metabolism*; D008139:Loperamide / Q000494:pharmacology*; D009270:Naloxone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects*; D015398:Signal Transduction / Q000187:drug effects; D013997:Time Factors; D014268:Trifluoperazine / Q000494:pharmacology; D014700:Verapamil / Q000494:pharmacology
D000930:Antidiarrheals; D002121:Calcium Channel Blockers; D002147:Calmodulin; D002712:Chlorides; D018679:Cholinergic Agonists; D009292:Narcotic Antagonists; D015221:Potassium Channels; D005576:Colforsin; D014268:Trifluoperazine; D009270:Naloxone; D008139:Loperamide; D002217:Carbachol; D014700:Verapamil