Satlin L M, Schwartz G J
Department of Pediatrics, Albert Einstein College of Medicine, Bronx, New York 10461.
J Cell Biol. 1989 Sep;109(3):1279-88. doi: 10.1083/jcb.109.3.1279.
The renal cortical collecting duct (CCD) consists of principal and intercalated cells. Two forms of intercalated cells, those cells involved in H+/HCO3- transport, have recently been described. H+-secreting cells are capable of apical endocytosis and have H+ATPase on the apical membrane and a basolateral Cl-/HCO3- exchanger. HCO3(-)-secreting cells bind peanut agglutinin (PNA) to apical membrane receptors and have diffuse or basolateral distribution of H+ATPase; their Cl-/HCO3- exchanger is on the apical membrane. We found that 20 h after acid feeding of rabbits, there was a fourfold increase in number of cells showing apical endocytosis and a numerically similar reduction of cells binding PNA. Incubation of CCDs at pH 7.1 for 3-5 h in vitro led to similar, albeit less pronounced, changes. Evidence to suggest internalization and degradation of the PNA binding sites included a reduction in apical binding of PNA, decrease in pH in the environment of PNA binding, and incorporation of electron-dense PNA into cytoplasmic vesicles. Such remodeling was dependent on protein synthesis. There was also functional evidence for loss of apical Cl-/HCO3- exchange on PNA-labeled cells. Finally, net HCO3- flux converted from secretion to absorption after incubation at low pH. Thus, exposure of CCDs to low pH stimulates the removal/inactivation of apical Cl-/HCO3- exchangers and the internalization of other apical membrane components. Remodeling of PNA-labeled cells may mediate the change in polarity of HCO3- flux observed in response to acid treatment.
肾皮质集合管（CCD）由主细胞和闰细胞组成。最近发现了两种参与H⁺/HCO₃⁻转运的闰细胞形式。分泌H⁺的细胞能够进行顶端内吞作用，在顶端膜上有H⁺ATP酶，在基底外侧有Cl⁻/HCO₃⁻交换体。分泌HCO₃⁻的细胞将花生凝集素（PNA）与顶端膜受体结合，H⁺ATP酶呈弥散或基底外侧分布；它们的Cl⁻/HCO₃⁻交换体在顶端膜上。我们发现，给兔子喂食酸20小时后，显示顶端内吞作用的细胞数量增加了四倍，而结合PNA的细胞数量在数值上有类似的减少。将CCD在体外pH 7.1条件下孵育3 - 5小时会导致类似但不太明显的变化。表明PNA结合位点内化和降解的证据包括PNA顶端结合减少、PNA结合环境中的pH降低以及电子致密的PNA掺入细胞质小泡。这种重塑依赖于蛋白质合成。在PNA标记的细胞上也有顶端Cl⁻/HCO₃⁻交换丧失的功能证据。最后，在低pH孵育后，HCO₃⁻净通量从分泌转变为吸收。因此，将CCD暴露于低pH会刺激顶端Cl⁻/HCO₃⁻交换体的去除/失活以及其他顶端膜成分的内化。PNA标记细胞的重塑可能介导了在酸处理后观察到的HCO₃⁻通量极性变化。
