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Chloride channels and anion fluxes in a human colonic epithelium (HCA‐7)
Author(s) -
Henderson R.M.,
Ashford M.L.J.,
MacVinish L.J.,
Cuthbert A.W.
Publication year - 1992
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1992.tb14301.x
Subject(s) - chemistry , forskolin , bapta , dids , intracellular , chloride channel , biophysics , efflux , membrane potential , chloride , apical membrane , conductance , calcium , ion transporter , depolarization , adenosine , biochemistry , membrane , biology , receptor , mathematics , organic chemistry , combinatorics
1 Colonic epithelial cells, derived from a human adenocarcinoma (HCA‐7), were examined by the patch clamp technique. 2 Outwardly rectifying anion (Cl − ) channels were identified in the apical membrane. The conductance was g in ≅ 26 pS, g out ≅ 40 pS. The open state probability of the channels increased with depolarization and the selectivity for Cl − over K + (P Cl /P K ) was ≅ 7.5. 3 The channels were sensitive to intracellular adenosine 3′:5′‐cyclic monophosphate (cyclic AMP, 0.1 m m ), but not to Ca 2+ (at concentrations up to 1 m m ). At depolarized potentials the channels were blocked by pirentanide (1–5 μ m ) applied intracellularly. 4 HCA‐7 monolayers loaded with 125 I − (as a marker for Cl − ) were used to measure I − efflux and converted to instantaneous rate constants. 5 The rate constant for I − efflux was increased by forskolin and lysylbradykinin (LBK). The effects of forskolin were not effected by BAPTA (an intracellular calcium chelator). The effects of LBK were inhibited by BAPTA and by Ba 2+ , indicating that LBK raised intracellular Ca 2+ (Ca i ) which activates Ca 2+ ‐sensitive K‐channels, the latter being blocked by Ba 2+ . 6 Although it cannot be conclusively proved that the outwardly rectifying chloride channels described here are solely or partially responsible for the increased anion efflux or transepithelial chloride secretion, the channels are likely to be more relevant for cyclic AMP‐requiring rather than Ca 2+ ‐requiring secretagogues.