Oppermann Mona, Mizel Diane, Huang George, Li Cuiling, Deng Chuxia, Theilig Franziska, Bachmann Sebastian, Briggs Josie, Schnermann Jurgen, Castrop Hayo
National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892-1370, USA.
J Am Soc Nephrol. 2006 Aug;17(8):2143-52. doi: 10.1681/ASN.2006040384. Epub 2006 Jun 28.
Na,K,2Cl co-transporter (NKCC2), the primary NaCl uptake pathway in the thick ascending limb of Henle, is expressed in three different full-length splice variants, called NKCC2F, NKCC2A, and NKCC2B. These variants, derived by differential splicing of the variable exon 4, show a distinct distribution pattern along the loop of Henle, but the functional significance of this organization is unclear. By introduction of premature stop codons into exon 4B, specific for the B isoform, mice with an exclusive NKCC2B deficiency were generated. Relative expression levels and distribution patterns of NKCC2A and NKCC2F were not altered in the NKCC2B-deficient mice. NKCC2B-deficient mice did not display a salt-losing phenotype; basal plasma renin and aldosterone levels were not different from those of wild-type mice. Ambient urine osmolarities, however, were slightly but significantly reduced. Distal Cl concentration was significantly elevated and loop of Henle Cl absorption was reduced in microperfused superficial loops of Henle of NKCC2B-deficient mice. Because of the presence of NKCC2A in the macula densa, maximum tubuloglomerular feedback responses were normal, but tubuloglomerular feedback function curves were right-shifted, indicating reduced sensitivity in the subnormal flow range. Plasma renin concentration in NKCC2B-deficient mice was reduced under conditions of salt loading compared with that in wild-type mice. This study shows the feasibility of generating mice with specific deletions of single splice variants. The mild phenotype of mice that are deficient in the B isoform of NKCC2 indicates a limited role for NKCC2B for overall salt retrieval. Nevertheless, the high-affinity NKCC2B contributes to salt absorption and macula densa function in the low NaCl concentration range.
钠钾氯共转运体（NKCC2）是亨利氏袢升支粗段主要的氯化钠摄取途径，以三种不同的全长剪接变体形式表达，分别称为NKCC2F、NKCC2A和NKCC2B。这些变体由可变外显子4的差异剪接产生，沿亨利氏袢呈现出独特的分布模式，但这种组织形式的功能意义尚不清楚。通过在特定于B异构体的外显子4B中引入提前终止密码子，产生了仅缺乏NKCC2B的小鼠。在NKCC2B缺陷型小鼠中，NKCC2A和NKCC2F的相对表达水平和分布模式未发生改变。NKCC2B缺陷型小鼠未表现出失盐表型；基础血浆肾素和醛固酮水平与野生型小鼠无异。然而，周围尿渗透压略有但显著降低。在NKCC2B缺陷型小鼠的微灌注浅表亨利氏袢中，远端氯离子浓度显著升高，亨利氏袢氯离子吸收减少。由于致密斑中存在NKCC2A，最大管球反馈反应正常，但管球反馈功能曲线右移，表明在低于正常流量范围内敏感性降低。与野生型小鼠相比，在盐负荷条件下，NKCC2B缺陷型小鼠的血浆肾素浓度降低。本研究表明了产生特定剪接变体缺失小鼠的可行性。NKCC2的B异构体缺陷型小鼠的轻度表型表明NKCC2B在整体盐回收中的作用有限。尽管如此，高亲和力的NKCC2B在低氯化钠浓度范围内有助于盐吸收和致密斑功能。
