Bicarbonate-dependent chloride absorption in small intestine: Ion fluxes and intracellular chloride activities |
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Authors: | John F White |
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Institution: | (1) Department of Physiology, Emory University, 30322 Atlanta, Georgia |
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Abstract: | Summary Proximal, stripped segments of small intestine from the urodeleAmphiuma were short-circuited in media containing Na+, Cl– and HCO
3
–
. Under these conditions there was a large net absorption of Cl–, a small net absorption of Na+ and a residual flux (J
Net
R
) consistent with HCO
3
–
secretion. Net Cl– absorption correlated with the short-circuit current (I
sc); net Na+ absorption correlated negatively withJ
Net
R
. Acetazolamide eliminated theI
sc, lowered Cl– absorption by 50%, and reduced net Na+ absorption without alteringJ
Net
R
. Benzolamide inhibited theI
sc without alteringJ
Net
R
. Benzolamide inhibited theI
sc more rapidly when applied on the mucosal surface. Replacement of Na+ or HCO
3
–
(and CO2) in the media eliminated theI
sc, net Cl– absorption and the residual flux. Likewise, inclusion of the stilbene SITS in the serosal media eliminated theI
sc, net Cl– absorption and the residual flux. The cytoplasmic activity of Cl– (a
ci
a
) was determined with single and double-barreled microelectrodes. Thea
ci
a
of villus absorptive cells in normal media was 21.0mm and in excess of that expected on the basis of electrochemical equilibrium of Cl– at the mucosal membrane. Active Cl– accumulation was also observed in the presence of acetazolamide but was eliminated upon replacement of media Na+ with choline. The mucosal membrane potential was depolarized upon replacement of media Na+. It is concluded that Cl– is actively absorbed into intestinal cells ofAmphiuma by an electrogenic process located in the mucosal membrane. Depending on the level of intracellular HCO
3
–
, accumulated Cl– may diffuse passively back into the mucosal media or undergo exchange with bath HCO
3
–
at the serosal membrane. |
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Keywords: | |
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