期刊
PFLUGERS ARCHIV-EUROPEAN JOURNAL OF PHYSIOLOGY
卷 454, 期 3, 页码 441-450出版社
SPRINGER HEIDELBERG
DOI: 10.1007/s00424-007-0213-7
关键词
(CT)-C-36 uptake; stable expression; intracellular pH (pH(i)); pHi-dependent; carrier-mediated; anion transporter
类别
资金
- NIDDK NIH HHS [DK60069] Funding Source: Medline
- Wellcome Trust Funding Source: Medline
Studies with apical membrane vesicles have shown that two distinct and separate anion exchange processes are present in rat distal colon, 4,4'- diisothiocyanatostilbene2,2'- disulfonic acid ( DIDS)- sensitive Cl- - HCO3- exchange, and DIDS- resistant Cl- - OH- exchange. These studies proposed that anion exchanger (AE)-1 isoform encodes the former as both apical membrane DIDS- sensitive Cl- - HCO3- exchange, and AE1 specific mRNA are present only in surface cells and are down-regulated in Na-depleted rats, whereas downregulated in adenoma (DRA) encodes the latter as both DIDS- resistant Cl- - OH- exchange, and DRA- specific proteins are present in apical membranes of both surface and crypt cells and are not altered in Na+- depleted rats. Studies were, therefore, initiated to identify the function of rat DRA ( rDRA) in vitro. rDRA cDNA isolated from rat distal colon encodes a 757-amino-acid protein which has 96 and 81% homology with mDRA and hDRA, respectively. rDRA-specific mRNA expression was detectable only in specific segments of the digestive tract ( duodenum, ileum, cecum, proximal colon, and distal colon) but not in the stomach, jejunum, or in the kidney, brain, heart, and lung. HEK 293 cells stably transfected with rDRA exhibited DIDS- insensitive and intracellular acid pH (pHi 6.5)-sensitive Cl uptake that: ( 1) was significantly stimulated by outward Cl-, HCO3-, isobutyrate, and possibly OH- gradients; ( 2) was saturated as a function of increasing extracellular Cl concentrations with an apparent K-m for Cl of 2.9 +/- 0.3 mM; and ( 3) was inhibited competitively by extracellular oxalate but not by SO42-. A high rate of DIDS- insensitive Cl influx at pH 6.5 was also present under physiological Cl- concentration. Our observations that rDRA mediates DIDS- insensitive, acid pH- dependent Cl- uptake are consistent with prior observations that rDRA does not mediate DIDS- sensitive Cl- - HCO3- exchange in rat distal colon. We speculate that, in addition to mediating pH- sensitive Cl- uptake, rDRA may function as a modifier of other anion transport proteins.
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