Department of Physiology and Biophysics, Institute of Biomedical Sciences, University of São Paulo, São Paulo, Brazil.
J Nephrol. 2010 Nov-Dec;23 Suppl 16:S19-27.
The functional versatility of the distal nephron is mainly due to the large cytological heterogeneity of the segment. Part of Na+ uptake by distal tubules is dependent on Na+/H+ exchanger 2 (NHE2), implicating a role of distal convoluted cells also in acid-base homeostasis. In addition, intercalated (IC) cells expressed in distal convoluted tubules, connecting tubules and collecting ducts are involved in the final regulation of acid-base excretion. IC cells regulate acid-base handling by 2 main transport proteins, a V-type H+-ATPase and a Cl/HCO3- exchanger, localized at different membrane domains. Type A IC cells are characterized by a luminal H+-ATPase in series with a basolateral Cl/HCO3- exchanger, the anion exchanger AE1. Type B IC cells mediate HCO3- secretion through the apical Cl-/HCO3- exchanger pendrin in series with a H+-ATPase at the basolateral membrane. Alternatively, H+/K+-ATPases have also been found in several distal tubule cells, particularly in type A and B IC cells. All of these mechanisms are finely regulated, and mutations of 1 or more proteins ultimately lead to expressive disorders of acid-base balance.
远曲小管的功能多样性主要归因于其节段的巨大细胞学异质性。部分远曲小管对 Na+的摄取依赖于 Na+/H+交换器 2（NHE2），这意味着远曲的浓缩细胞在酸碱平衡中也具有作用。此外，在远曲小管、连接小管和集合管中表达的闰细胞也参与了酸碱排泄的最终调节。闰细胞通过 2 种主要的转运蛋白来调节酸碱处理，即位于不同膜域的 V 型 H+-ATP 酶和 Cl-/HCO3-交换器。A型闰细胞的特征是腔侧 H+-ATP 酶与基底外侧 Cl-/HCO3-交换器 AE1 串联。B 型闰细胞通过顶端 Cl-/HCO3-交换器 pendrin 与基底外侧膜的 H+-ATP 酶串联介导 HCO3-分泌。另外，在几个远曲小管细胞中也发现了 H+/K+-ATP 酶，特别是在 A 型和 B 型闰细胞中。所有这些机制都受到精细调节，而 1 种或多种蛋白质的突变最终会导致酸碱平衡的表达紊乱。
