Al-Awqati Q
College of Physicians and Surgeons of Columbia University, New York, New York 10032, USA.
Am J Physiol. 1996 Jun;270(6 Pt 1):C1571-80. doi: 10.1152/ajpcell.1996.270.6.C1571.
The intercalated cell is an epithelial cell of the renal collecting tubule that is specialized for H+ and HCO3- transport. These cells exist as two types, alpha and beta. The alpha-cell secretes H+ into the lumen by an apical H(+)-ATPase and a basolateral Cl-/HCO3- exchanger that is a form of band 3 protein (AE1). The beta-cell secretes HCO3- into the lumen by an apical Cl-/HCO3- exchanger and a basolateral H(+)-ATPase. In a previous study, it was suggested that a reversal in epithelial polarity of these cells occurs during the response of the kidney to an acid load (G.J. Schwartz, J. Barasch, and Q. Al-Awqati. Nature Lond. 318: 368-371, 1985). Recent studies, however have shown that there are many other subtypes where the distribution of these two proteins does not fit into this neat bipolar classification. This group of investigators recently generated an immortalized cell line of the beta-intercalated cell and found that the apical Cl-/HCO3- exchanger is also AE1. Furthermore, when these cells were seeded at high densities, the polarized targeting of the apical band 3 was reversed to the basolateral membrane. This was produced by the secretion of extracellular matrix protein that by themselves were capable of reversing the polarity of band 3 (J. S. van Adelsberg, J. C. Edwards, J. Takito, B. Kiss, and Q. Al-Awqati. Cell 76: 1053-1061, 1995). A large new extracellular matrix protein, hensin, was identified and found to be present exclusively in the collecting tubule. The extensive recent literature on the biology of alpha- and beta-intercalated cells is reviewed here and found to be compatible with the idea of the reversal of polarity as a mechanism for the regulation of H+ secretion by the tubule.
闰细胞是肾集合管的一种上皮细胞，专门负责H⁺和HCO₃⁻的转运。这些细胞有α和β两种类型。α细胞通过顶端的H⁺-ATP酶和基底外侧的Cl⁻/HCO₃⁻交换体（一种带3蛋白形式，即AE1）将H⁺分泌到管腔中。β细胞通过顶端的Cl⁻/HCO₃⁻交换体和基底外侧的H⁺-ATP酶将HCO₃⁻分泌到管腔中。在先前的一项研究中，有人提出在肾脏对酸负荷的反应过程中，这些细胞的上皮极性会发生逆转（G.J.施瓦茨、J.巴拉施和Q.阿勒-奥瓦蒂。《自然》伦敦版318: 368 - 371, 1985）。然而，最近的研究表明，还有许多其他亚型，这两种蛋白的分布并不符合这种简单的双极分类。这组研究人员最近建立了一种β闰细胞的永生化细胞系，发现顶端的Cl⁻/HCO₃⁻交换体也是AE1。此外，当这些细胞以高密度接种时，顶端带3的极性靶向会逆转至基底外侧膜。这是由细胞外基质蛋白的分泌导致的，这些蛋白自身能够逆转带3的极性（J.S.范·阿德尔伯格、J.C.爱德华兹、J. taki to、B.基斯和Q.阿勒-奥瓦蒂。《细胞》76: 1053 - 1061, 1995）。一种新的大型细胞外基质蛋白——hensin被鉴定出来，发现它仅存在于集合管中。这里回顾了最近关于α和β闰细胞生物学的大量文献，发现其与极性逆转作为小管调节H⁺分泌机制的观点相符。
