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Departments of 1 Internal Medicine and 2 Surgery, Yale University, New Haven, Connecticut 06520
A novel Cl-dependent Na/H exchange (Cl-NHE) has been identified in apical membranes of crypt cells of rat distal colon. The presence of Cl is required for both outward proton gradient-driven Na uptake in apical membrane vesicles (AMV) and Na-dependent intracellular pH recovery from an acid load in the crypt gland. The present study establishes that Cl-dependent outward proton gradient-driven 22Na uptake 1) is saturated with increasing extravesicular Na concentration with a Michaelis constant (Km) for Na of ~24.2 mM; 2) is saturated with increasing outward H concentration gradient with a hyperbolic curve and a Km for H of ~1.5 µM; 3) is inhibited by the Na/H exchange (NHE) inhibitors amiloride, ethylisopropylamiloride, and HOE-694 with an inhibitory constant (Ki) of ~480.2, 1.1, and 9.5 µM, respectively; 4) is inhibited by 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid, an anion exchange inhibitor at low concentration and a Cl channel blocker at high dose, and by 5-nitro-2(3-phenylpropylamino)benzoic acid, a Cl channel blocker, with a Ki of ~280.6 and 18.3 µM, respectively; and 5) substantially stimulated Cl-NHE activity by dietary Na depletion, which increases plasma aldosterone and inhibits NHE in surface cell AMV. These properties of Cl-NHE are distinct from those of NHE1, NHE2, and NHE3 isoforms that are present in colonic epithelial cells; thus these results suggest that the colonic crypt cell Cl-NHE is a novel NHE isoform.
sodium depletion; aldosterone; regulation; kinetics
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