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Am J Physiol Gastrointest Liver Physiol 272: G435-G445, 1997;
0193-1857/97 $5.00
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AJP - Gastrointestinal and Liver Physiology, Vol 272, Issue 3 435-G445, Copyright © 1997 by American Physiological Society

ARTICLES

Differing mechanisms of stimulation of Na+ absorption in rabbit proximal colon

J. H. Sellin and R. Desoignie
Department of Internal Medicine, The University of Texas Medical School at Houston, 77030, USA.

Both alpha2-adrenergic agonists and decreased Na+ in the bathing fluids stimulate electroneutral Na+ absorption in rabbit proximal colon, but it is unclear whether they have similar modes of action. We sought to define regulatory events involved with stimulation of Na+ absorption by these two agonists. Transport parameters were assessed by ion flux studies under short-circuit and pH stat conditions, recordings of intracellular electrical potential difference (psi(mc)) with microelectrode impalements, and measurement of intracellular pH (pH(i)). Epinephrine elicited a yohimbine-inhibitable alkalinization of pH(i) but did not alter psi(mc) In contrast, lowered serosal Na+ concentration ([Na+]) did not significantly increase pH(i) but did depolarize psi(mc). Removal of serosal HCO(3)- stimulated Na+ absorption and reversed residual ion flux from secretion to absorption. pH stat studies demonstrated epinephrine-stimulated, amiloride-inhibitable serosal alkalinization. Serosal 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid inhibited Na+ absorption. Epinephrine and lowered [Na+] have different effects on intracellular parameters associated with electroneutral Na+ absorption. Epinephrine stimulates an apical Na+/H+ exchanger. Lowered [Na+] elicits responses consistent with a coupled Na+-HCO(3x)- exit step. Coordinated function of apical Na+/H+ exchangers and a basolateral Na+-HCO(3)(x)- symport permit Cl(-)-independent electroneutral Na+ absorption while maintaining pH(i) homeostasis. Given the low [Cl-] environment of the colonic lumen, this transport pathway may be important for electroneutral Na+ absorption.


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 Am. J. Physiol. Gastrointest. Liver Physiol.Home page
M. W. Musch, C. Bookstein, Y. Xie, J. H. Sellin, and E. B. Chang
SCFA increase intestinal Na absorption by induction of NHE3 in rat colon and human intestinal C2/bbe cells
Am J Physiol Gastrointest Liver Physiol, April 1, 2001; 280(4): G687 - G693.
[Abstract] [Full Text] [PDF]


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