Malnic G, Fernandez R, Lopes M J
Departamento de Fisiologia e Biofísica, Universidade de São Paulo, Brasil.
Braz J Med Biol Res. 1994 Apr;27(4):831-50.
The present paper reviews mechanisms by which the kidney controls systemic acid-base balance, with emphasis on the role of the distal nephron, and particularly of the cortical distal tubule. These mechanisms are essentially based on H-ion transport along the whole nephron. In proximal tubule cells, approximately 80% of H-ion secretion is mediated by Na+/H+ exchange, and 20% by H(+)-ATPase. In the distal nephron, acid-base transport mechanisms are located mainly in intercalated cells. H-ion secretion is effected by vacuolar H(+)-ATPase in alpha-intercalated cells and, in K-depleted animals, also by the gastric type H/K ATPase. In animals in alkalosis, beta-intercalated cells secrete bicarbonate by an apical Cl-/HCO3- exchanger, while a basolateral H-ATPase transfers H-ions into the interstitium. In cortical distal tubule, these mechanisms have been shown to be present in the intercalated cells of the connecting segment and of the initial collecting duct (the late distal tubule of micropuncture experiments). In the convoluted distal tubule (early distal tubule), most H-ion secretion occurs by means of the Na+/H+ exchanger. These data show that the distal nephron, including the cortical distal tubule, is a nephron segment responsible for a sizeable portion of bicarbonate reabsorption and titratable acid generation, as well as for bicarbonate secretion under appropriate metabolic conditions, being therefore the site of fine regulation of renal mechanisms that maintain acid-base homeostasis.
本文综述了肾脏控制全身酸碱平衡的机制，重点关注远端肾单位的作用，特别是皮质远端小管的作用。这些机制主要基于整个肾单位的氢离子转运。在近端小管细胞中，约80%的氢离子分泌由Na+/H+交换介导，20%由H(+)-ATP酶介导。在远端肾单位，酸碱转运机制主要位于闰细胞中。氢离子分泌由α-闰细胞中的液泡H(+)-ATP酶实现，在低钾动物中，也由胃型H/K ATP酶实现。在碱中毒动物中，β-闰细胞通过顶端Cl-/HCO3-交换体分泌碳酸氢盐，而基底外侧H-ATP酶将氢离子转运到间质中。在皮质远端小管中，这些机制已被证明存在于连接段和初始集合管（微穿刺实验中的远端小管晚期）的闰细胞中。在曲部远端小管（远端小管早期），大多数氢离子分泌通过Na+/H+交换体进行。这些数据表明，包括皮质远端小管在内的远端肾单位是肾单位的一个节段，负责相当一部分碳酸氢盐的重吸收和可滴定酸的生成，以及在适当的代谢条件下分泌碳酸氢盐，因此是维持酸碱平衡的肾脏机制精细调节的部位。
