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标题：Sialin (SLC17A5) functions as a nitrate transporter in the plasma membrane
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作者：Lizheng Qin ; Xibao Liu ; Qifei Sun 等
期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2012
卷号：109
期号：33
页码：13434-13439
DOI：10.1073/pnas.1116633109
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：In vivo recycling of nitrate (NO3-) and nitrite (NO2-) is an important alternative pathway for the generation of nitric oxide (NO) and maintenance of systemic nitrate-nitrite-NO balance. More than 25% of the circulating NO3- is actively removed and secreted by salivary glands. Oral commensal bacteria convert salivary NO3- to NO2-, which enters circulation and leads to NO generation. The transporters for NO3- in salivary glands have not yet been identified. Here we report that sialin (SLC17A5), mutations in which cause Salla disease and infantile sialic acid storage disorder (ISSD), functions as an electrogenic 2NO3-/H+ cotransporter in the plasma membrane of salivary gland acinar cells. We have identified an extracellular pH-dependent anion current that is carried by NO3- or sialic acid (SA), but not by Br-, and is accompanied by intracellular acidification. Both responses were reduced by knockdown of sialin expression and increased by the plasma membrane-targeted sialin mutant (L22A-L23A). Fibroblasts from patients with ISSD displayed reduced SA- and NO3--induced currents compared with healthy controls. Furthermore, expression of disease-associated sialin mutants in fibroblasts and salivary gland cells suppressed the H+-dependent NO3- conductance. Importantly, adenovirus-dependent expression of the sialinH183R mutant in vivo in pig salivary glands decreased NO3- secretion in saliva after intake of a NO3--rich diet. Taken together, these data demonstrate that sialin mediates nitrate influx into salivary gland and other cell types. We suggest that the 2NO3-/H+ transport function of sialin in salivary glands can contribute significantly to clearance of serum nitrate, as well as nitrate recycling and physiological nitrite-NO homeostasis.
关键词：pH ; proton