Flagella M, Clarke L L, Miller M L, Erway L C, Giannella R A, Andringa A, Gawenis L R, Kramer J, Duffy J J, Doetschman T, Lorenz J N, Yamoah E N, Cardell E L, Shull G E
Department of Molecular Genetics, Biochemistry and Microbiology, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267, USA.
J Biol Chem. 1999 Sep 17;274(38):26946-55. doi: 10.1074/jbc.274.38.26946.
In chloride-secretory epithelia, the basolateral Na-K-2Cl cotransporter (NKCC1) is thought to play a major role in transepithelial Cl(-) and fluid transport. Similarly, in marginal cells of the inner ear, NKCC1 has been proposed as a component of the entry pathway for K(+) that is secreted into the endolymph, thus playing a critical role in hearing. To test these hypotheses, we generated and analyzed an NKCC1-deficient mouse. Homozygous mutant (Nkcc1(-/-)) mice exhibited growth retardation, a 28% incidence of death around the time of weaning, and mild difficulties in maintaining their balance. Mean arterial blood pressure was significantly reduced in both heterozygous and homozygous mutants, indicating an important function for NKCC1 in the maintenance of blood pressure. cAMP-induced short circuit currents, which are dependent on the CFTR Cl(-) channel, were reduced in jejunum, cecum, and trachea of Nkcc1(-/-) mice, indicating that NKCC1 contributes to cAMP-induced Cl(-) secretion. In contrast, secretion of gastric acid in adult Nkcc1(-/-) stomachs and enterotoxin-stimulated fluid secretion in the intestine of suckling Nkcc1(-/-) mice were normal. Finally, homozygous mutants were deaf, and histological analysis of the inner ear revealed a collapse of the membranous labyrinth, consistent with a critical role for NKCC1 in transepithelial K(+) movements involved in generation of the K(+)-rich endolymph and the endocochlear potential.
在氯离子分泌上皮细胞中，基底外侧钠-钾-2氯协同转运蛋白（NKCC1）被认为在跨上皮氯离子和液体转运中起主要作用。同样，在内耳的边缘细胞中，NKCC1被认为是钾离子进入途径的一个组成部分，钾离子被分泌到内淋巴中，因此在听力中起关键作用。为了验证这些假设，我们生成并分析了一只NKCC1基因缺失的小鼠。纯合突变体（Nkcc1-/-）小鼠表现出生长迟缓，在断奶时约有28%的死亡率，并且在维持平衡方面有轻度困难。杂合子和纯合子突变体的平均动脉血压均显著降低，表明NKCC1在维持血压方面具有重要功能。依赖于CFTR氯离子通道的cAMP诱导的短路电流在Nkcc1-/-小鼠的空肠、盲肠和气管中降低，表明NKCC1有助于cAMP诱导的氯离子分泌。相比之下，成年Nkcc1-/-小鼠胃中的胃酸分泌以及哺乳期Nkcc1-/-小鼠肠道中肠毒素刺激的液体分泌均正常。最后，纯合突变体耳聋，内耳的组织学分析显示膜迷路塌陷，这与NKCC1在参与产生富含钾离子的内淋巴和内耳蜗电位的跨上皮钾离子运动中起关键作用一致。
