Nakamura N, Suzuki Y, Sakuta H, Ookata K, Kawahara K, Hirose S
Department of Biological Sciences, Tokyo Institute of Technology, Yokohama 226-8501, Japan.
Biochem J. 1999 Sep 1;342 ( Pt 2)(Pt 2):329-36.
A novel inwardly rectifying K+ channel, Kir7.1, with unique pore properties, was cloned recently. Working in the field of osmoregulation, we have also identified the same human and rat channel and found that the channel is unique not only in its pore sequence but also in its dense localization in the follicular cells of the thyroid gland. Northern blot analysis revealed that the channel message was abundantly expressed in the thyroid gland and small intestine, and moderately in the kidney, stomach, spinal cord and brain. Immunohistochemistry of the rat thyroid, intestine and choroid plexus demonstrated the expression of the channel protein in the follicular cells and epithelial cells, suggesting a role in the regulation of the ion-transporting functions of these specialized cells. The unique pore properties of Kir7.1 make it a strong candidate for the hypothetical low-conductance K+ channel that is functionally coupled with Na+,K(+)-ATPase by recycling K+. We therefore further examined the co-localization of Kir7.1 and Na+,K(+)-ATPase and found that both are localized in the basolateral membrane of the thyroid follicular cell; in the choroid plexus, which is known to be unique in having Na+,K(+)-ATPase in the apical side of the epithelial cells, Kir7.1 was found in the apical membrane, implying a close functional coupling between the channel and Na+,K(+)-ATPase.
最近克隆出一种具有独特孔道特性的新型内向整流钾离子通道Kir7.1。在渗透调节领域开展研究时，我们也鉴定出了相同的人类和大鼠通道，并发现该通道不仅在其孔道序列方面独特，而且在甲状腺滤泡细胞中高度富集。Northern印迹分析显示，该通道的信使RNA在甲状腺和小肠中大量表达，在肾脏、胃、脊髓和脑中中度表达。对大鼠甲状腺、肠道和脉络丛进行免疫组织化学分析表明，该通道蛋白在滤泡细胞和上皮细胞中表达，提示其在调节这些特化细胞的离子转运功能中发挥作用。Kir7.1独特的孔道特性使其成为假想的低电导钾离子通道的有力候选者，该通道通过钾离子循环与钠钾ATP酶功能偶联。因此，我们进一步研究了Kir7.1与钠钾ATP酶的共定位情况，发现二者均定位于甲状腺滤泡细胞的基底外侧膜；在脉络丛中，已知其上皮细胞顶端存在钠钾ATP酶，而Kir7.1定位于顶端膜，这意味着该通道与钠钾ATP酶之间存在紧密的功能偶联。
