Electrogenic Na+ absorption of rat distal colon is confined to surface epithelium: a voltage-scanning study

Am J Physiol. 1993 May;264(5 Pt 1):C1285-93. doi: 10.1152/ajpcell.1993.264.5.C1285.


There is no quantitative assignment of large intestinal electrogenic Na+ absorption to surface epithelium and crypts so far. We determined the spatial distribution of electrogenic Na+ absorption to crypts and surface epithelium of rat late distal colon using a modified voltage-scanning technique. Voltage deflections resulting from external 30-Hz current were sensed by an extracellular microelectrode stepping at 0.7 Hz above crypt openings or surface epithelium. Local conductances were calculated applying a planar model of electrical field distribution to surface epithelium and a electrostatic disk source model to the crypts. These models were confirmed by methodological experiments where the electrode position was varied in vertical and horizontal direction. Electrogenic Na+ absorption was detected by blocking apical Na+ channels by mucosal 0.1 mM amiloride. Under control conditions surface epithelium contributed 44% (2.0 +/- 0.2 mS/cm2) and crypts 56% (2.6 +/- 0.2 mS/cm2) to the total conductance of 4.6 +/- 0.4 mS/cm2. Electrogenic Na+ absorption was induced by 6 h in vitro incubation in a medium containing 3 nM aldosterone. This caused a short-circuit current (ISC) of 12.1 +/- 0.8 mumol.h-1.cm-2, which was paralleled by a 2.5-fold increase in surface epithelial conductance to 5.1 +/- 0.4 mS/cm2, whereas crypt conductance was not significantly altered (3.0 +/- 0.2 mS/cm2). Amiloride reversed ISC to -0.8 +/- 0.1 mumol.-1.cm-2 and decreased surface epithelium conductance to 2.3 +/- 0.3 mS/cm2 but again had no significant effect on crypt conductance (2.5 +/- 0.3 mS/cm2). Sham incubation (no hormones added) for 6 h neither induced electrogenic transport nor altered local epithelial conductances.(ABSTRACT TRUNCATED AT 250 WORDS)

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aldosterone / pharmacology
  • Amiloride / pharmacology
  • Animals
  • Biological Transport / drug effects
  • Colon / physiology*
  • Electric Conductivity / drug effects
  • Electrophysiology / instrumentation
  • Electrophysiology / methods
  • Epithelium / drug effects
  • Epithelium / physiology
  • In Vitro Techniques
  • Intestinal Absorption* / drug effects
  • Intestinal Mucosa / drug effects
  • Intestinal Mucosa / physiology*
  • Male
  • Mathematics
  • Models, Biological
  • Rats
  • Rats, Wistar
  • Sodium / metabolism*


  • Aldosterone
  • Amiloride
  • Sodium