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

Author:

Sellin J. H.1,Desoignie R.1

Affiliation:

1. Department of Internal Medicine, The University of Texas MedicalSchool at Houston, 77030, USA.

Abstract

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.

Publisher

American Physiological Society

Subject

Physiology (medical),Gastroenterology,Hepatology,Physiology

Cited by 7 articles. 订阅此论文施引文献 订阅此论文施引文献,注册后可以免费订阅5篇论文的施引文献,订阅后可以查看论文全部施引文献

1. Physiology and Pathophysiology of Potassium Channels in Gastrointestinal Epithelia;Physiological Reviews;2008-07

2. Adrenoceptor heterogeneity in the ruminal epithelium of sheep;Journal of Comparative Physiology B;2005-04-01

3. Intracellular pH regulation in colonocytes of rat proximal colon;Biochimica et Biophysica Acta (BBA) - Molecular Basis of Disease;2001-05

4. SCFA increase intestinal Na absorption by induction of NHE3 in rat colon and human intestinal C2/bbe cells;American Journal of Physiology-Gastrointestinal and Liver Physiology;2001-04-01

5. Surface pH at the Basolateral Membrane of the Caecal Mucosa of Guinea Pig;Journal of Membrane Biology;1999-05-15

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