Abstract
The mechanism of sodium movement across apical membrane of colonic crypt cells of rat distal colon was examined in studies of both 22Na uptake by apical membrane vesicles (AMV) and the rate of intracellular pH (pHi) recovery from an acid load by the addition of lumen sodium. In the presence of chloride but not in its absence, 22Na uptake in crypt AMV was stimulated by an outward gradient of either [H+] or [Na+]. 22Na uptake stimulated by an outward [Na+] gradient was also observed in the presence of other halides in the order of chloride > bromide > fluoride > iodide. pHi recovery from an acid load was both lumen sodium- and chloride-dependent, and the rate of pHi recovery by lumen sodium in the presence of chloride was 65-fold greater than that in the absence of chloride (dpH/dt is 655.4 and 10.2 in the presence and absence of chloride, respectively). One mM amiloride inhibited both [H+] gradient-stimulated 22Na uptake in the presence of chloride in crypt AMV (80%) and lumen sodium- and chloride-dependent pHi recovery in crypt cells (96%). [H+] gradient stimulation of 22Na uptake by crypt AMV in the presence of chloride was less sensitive to amiloride than amiloride inhibition of Na-H exchange in colonic surface AMV. These studies provide compelling evidence that a chloride-dependent Na-H exchange that is relatively amiloride-resistant is present in the apical membrane of colonic crypt cells. As prior studies have not identified a chloride-dependent Na-H exchange, the molecular and functional basis of this novel transport process is not known.
Highlights
From the Departments of :j:Internal Medicine, §Surgery, and llCellular and Molecular Physiology, Yale University, New Haven, Connecticut 06520
The mechanism of sodium movement across apical membrane of colonic crypt cells of rat distal colon was examined in studies of both 22Na uptake by apical membrane vesicles (AMY) and the rate of intracellular pH recovery from an acid load by the addition of lumen sodium
In the presence of chloride but not in its absence, 22Na uptake in crypt apical membrane vesicles (AMV) was stimulated by an outward gradient of either [H+] or [Na+]. 22Na uptake stimulated by an outward [Na+] gradient was observed in the presence of other halides in the order of chloride > bromide > fluoride > iodide. pHi recovery from an acid load was both lumen sodium- and chloridedependent, and the rate of pHi recovery by lumen sodium in the presence of chloride was 65-fold greater than that in the absence of chloride
Summary
From the Departments of :j:Internal Medicine, §Surgery, and llCellular and Molecular Physiology, Yale University, New Haven, Connecticut 06520. The mechanism of sodium movement across apical membrane of colonic crypt cells of rat distal colon was examined in studies of both 22Na uptake by apical membrane vesicles (AMY) and the rate of intracellular pH (pHi) recovery from an acid load by the addition of lumen sodium. [H+] gradient stimulation of 22Na uptake by crypt AMV in the presence of chloride was less sensitive to amiloride than amiloride inhibition of Na-H exchange in colonic surface AMY. These studies provide compelling evidence that a chloride-dependent Na-H exchange that is relatively amiloride-resistant is present in the apical membrane of colonic crypt cells. Identified on basolateral membranes of polar cells and plasma membranes of non-polar cells are critical in the regulation of several intracellular functions and are often referred to as having "housekeeper" functions, while apical membrane Na-H exchange has been linked to transepithelial sodium movement
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