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Department of Pharmacology, University of Cambridge, Cambridge CB2 1QJ, United Kingdom
1-Ethyl-2-benzimidazolone (EBIO) caused a sustained increase in
electrogenic Cl
secretion
in isolated mouse colon mucosae, an effect reduced by blocking
basolateral K+ channels. The
Ca2+-sensitive
K+ channel blocker charybdotoxin
(ChTX) and the cAMP-sensitive K+
channel blocker 293B were more effective when the other had been added
first, suggesting that both types of
K+ channel were activated. EBIO
did not cause Cl
secretion
in cystic fibrosis (CF) colonic epithelia. In apically permeabilized
colonic mucosae, EBIO increased the
K+ current when a concentration
gradient was imposed, an effect that was completely sensitive to
ChTX. No current sensitive to trans-6-cyano-4-(N-ethylsulfonyl-N-methylamino)-3-hydroxy-2,2-dimethylchromane (293B) was found in this condition. However, the presence of
basolateral cAMP-sensitive K+
channels was demonstrated by the development of a 293B-sensitive K+ current after cAMP application
in permeabilized mucosae. In isolated colonic crypts EBIO increased
cAMP content but had no effect on intracellular
Ca2+. It is concluded
that EBIO stimulates Cl
secretion by activating
Ca2+-sensitive and cAMP-sensitive
K+ channels, thereby
hyperpolarizing the apical membrane, which increases the electrical
gradient for Cl
efflux
through the CF transmembrane conductance regulator (CFTR). CFTR is also
activated by the accumulation of cAMP as well as by direct activation.
colonic electrogenic chloride secretion; cystic fibrosis transmembrane conductance regulator; charybdotoxin; 293B
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