Levamisole inhibits intestinal Cl- secretion via basolateral K+ channel blockade.
OBJECTIVE
Phenylimidazothiazoles have recently been shown to activate wild-type and mutant cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channels in transfected cells and were proposed as therapy for cystic fibrosis. The aim of this study was to investigate the effects of phenylimidazothiazoles on regulated transepithelial Cl- transport in intact epithelia.


METHODS
T84 intestinal epithelial cells grown on permeable supports and stripped human colonic mucosal sheets were studied by conventional current-voltage clamping. Selective permeabilization of apical or basolateral membranes with the monovalent ionophore nystatin was used to isolate basolateral K+ and apical Cl- channel activity, respectively. 86Rb+ uptake was assessed for Na/K/2Cl cotransporter and Na+,K(+)-adenosine triphosphatase activity.


RESULTS
In T84 monolayers and human colon, levamisole and its brominated derivative bromotetramisole failed to activate transepithelial secretion. In fact, these compounds dose-dependently inhibited secretory responses to the cyclic adenosine monophosphate agonist forskolin and the Ca2+ agonist carbachol. In permeabilized T84 monolayers, phenylimidazothiazoles weakly activated apical Cl- currents (consistent with their reported action on CFTR) and did not affect bumetanide-sensitive or bumetanide-insensitive 86+Rb+ uptake. Instead, they profoundly inhibited the basolateral Ba(2+)-sensitive and Ba(2+)-insensitive K+ currents.


CONCLUSIONS
Phenylimidazothiazoles block K+ channels required for Cl(-)-secretory responses elicited by diverse pathways in model epithelia and native colon, an effect that outweighs their ability to activate apical Cl- channels.
Mun
E C
EC
Department of Surgery, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts, USA.
Mayol
J M
JM
Riegler
M
M
O'Brien
T C
TC
Farokhzad
O C
OC
Song
J C
JC
Pothoulakis
C
C
Hrnjez
B J
BJ
Matthews
J B
JB
D002118:Calcium / Q000502:physiology; D002352:Carrier Proteins / Q000378:metabolism; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism* / Q000502:physiology; D005576:Colforsin / Q000494:pharmacology; D003106:Colon / Q000187:drug effects / Q000502:physiology; D004553:Electric Conductivity; D006801:Humans; D066298:In Vitro Techniques; D007413:Intestinal Mucosa / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D007978:Levamisole / Q000494:pharmacology*; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology; D028021:Sodium-Potassium-Chloride Symporters; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D013773:Tetramisole / Q000031:analogs & derivatives / Q000494:pharmacology
D002352:Carrier Proteins; D002712:Chlorides; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D028021:Sodium-Potassium-Chloride Symporters; D005576:Colforsin; D007978:Levamisole; C006226:4-bromotetramisole; D013773:Tetramisole; D000254:Sodium-Potassium-Exchanging ATPase; D002118:Calcium