AJP - Gastrointestinal and Liver Physiology, Vol 264, Issue 3 569-G575, Copyright © 1993 by American Physiological Society

ARTICLES

Effect of intracellular acidification on colonic NaCl absorption

P. C. Dagher, R. W. Egnor and A. N. Charney
Nephrology Section, Department of Veterans Affairs Medical Center, New York, New York 10010.

CO2 stimulates Na+ and Cl- absorption in rat distal colon. This is most likely due to intracellular generation of H+ and HCO3- and stimulation of apical Na(+)-H+ and Cl(-)-HCO3- exchangers. We examined whether intracellular acidification by means other than CO2 would also stimulate Na+ absorption. Stripped segments of distal colon from male Sprague-Dawley rats were studied under short-circuit conditions in Ussing chambers. Identically prepared tissues were used for intracellular pH (pHi) measurements with the pH-sensitive dye 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein. When the Ringer PCO2 was increased from 20 to 34 mmHg, pHi decreased from 7.50 +/- 0.04 to 7.35 +/- 0.04 and net Na absorption increased from 2.4 +/- 0.7 to 3.7 +/- 0.7 mu eq.cm-2 x h-1. A similar degree of intracellular acidification was obtained with 2.6 microM nigericin, but no stimulation of Na+ absorption was seen. When Ringer-HCO3- concentration was reduced from 39 to 11 mM at constant PCO2 = 35 mmHg, pHi decreased from 7.55 +/- 0.02 to 7.11 +/- 0.02 with no effect on net Na+ absorption. A similar reduction in pHi in a CO2-HCO3(-)-free, N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid-buffered Ringer also did not stimulate Na+ absorption. Methazolamide had no effect on steady-state pHi at any given PCO2 but caused marked reductions in net Na+ absorption (9.6 +/- 2.4 to 5.2 +/- 1.2 mu eq.cm-2 x h-1 at PCO2 = 70 mmHg). We conclude that Na+ absorption in rat distal colon is not stimulated by intracellular acidification per se but rather has an absolute requirement for CO2 and carbonic anhydrase activity.

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