Mechanisms of Na and Cl absorption across the distal colon epithelium of the pig

Timothy R. Traynor, Scott M O'Grady

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4 Scopus citations


Porcine distal colon epithelium was mounted in Ussing chambers and bathed in plasma-like Ringer solution. Tissue conductances ranged from 10 to 15 mS and the short-circuit current (Isc) ranged from-15 to 220 μA·cm-2. Variations in basal Isc resulted from differences in the amount of amiloride (10μM mucosal addition)-sensitive Na+ absorption. Ion substitution and transepithelial flux experiments showed that 10 μM amiloride produced a decrease in the mucosal-to-serosal (M-S) and net Na flux, and that this effect on Isc was independent of Cl- and HCO3-replacement. When the concentration of mucosal amiloride was increased from 10 to 100 μM, little change in Isc was observed. However, increasing the concentration to 1 m M produced a further inhibition, which often reversed the polarity of the Isc. The decrease in Isc due to 1 m M amiloride was dependent on both Cl- and HCO3-, and was attributed to reductions in the M-S and net Na+ fluxes as well as the M-S unidirectional Cl- flux. Ion replacement experiments demonstrated that Cl- substitution reduced the M-S and net Na fluxes, while replacement of HCO3-with HEPES abolished net Cl- absorption by reducing the M-S unidirectional Cl- flux. From these data it can be concluded that: (1) Na+ absorption is mediated by two distinct amiloride-sensitive transport pathways, and (2) Cl- absorption is completely HCO3--dependent (presumably mediated by Cl-/HCO3-exchange) and occurs independently of Na+ absorption.

Original languageEnglish (US)
Pages (from-to)47-53
Number of pages7
JournalJournal of Comparative Physiology B
Issue number1
StatePublished - Jan 1992


  • Cl-HCO exchange
  • HCO transport
  • Ion transport
  • Na channels
  • Na-H exchange
  • NaCl absorption


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