Weiner I D, Frank A E, Wingo C S
Division of Nephrology, Hypertension and Transplantation, University of Florida College of Medicine, Gainesville 32610, USA.
Am J Physiol. 1999 Apr;276(4):F606-13. doi: 10.1152/ajprenal.1999.276.4.F606.
The inner stripe of outer medullary collecting duct (OMCDis) is unique among collecting duct segments because both intercalated cells and principal cells secrete protons and reabsorb luminal bicarbonate. The current study characterized the mechanisms of OMCDis proton secretion. We used in vitro microperfusion, and we separately studied the principal cell and intercalated cell using differential uptake of the fluorescent, pH-sensitive dye, 2', 7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF). Both the principal cell and intercalated cell secreted protons, as identified as Na+/H+ exchange-independent intracellular pH (pHi) recovery from an intracellular acid load. Two proton transport activities were identified in the principal cell; one was luminal potassium dependent and Sch-28080 sensitive and the other was luminal potassium independent and luminal bafilomycin A1 sensitive. Thus the OMCDis principal cell expresses both apical H+-K+-ATPase and H+-ATPase activity. Intercalated cell Na+/H+ exchange-independent pHi recovery was approximately twice that of the principal cell and was mediated by pharmacologically similar mechanisms. We conclude 1) the OMCDis principal cell may contribute to both luminal potassium reabsorption and urinary acidification, roles fundamentally different from those of the principal cell in the cortical collecting duct; and 2) the OMCDis intercalated cell proton transporters are functionally similar to those in the principal cell, raising the possibility that an H+-K+-ATPase similar to the one present in the principal cell may contribute to intercalated cell proton secretion.
外髓集合管内带（OMCDis）在集合管各节段中独具特色，因为闰细胞和主细胞均可分泌质子并重吸收管腔内的碳酸氢盐。本研究对OMCDis分泌质子的机制进行了表征。我们采用体外微灌注技术，并利用对pH敏感的荧光染料2',7'-双（2-羧乙基）-5（6）-羧基荧光素（BCECF）吸光度的差异，分别对主细胞和闰细胞进行了研究。主细胞和闰细胞均能分泌质子，这可通过细胞内酸负荷后Na⁺/H⁺交换非依赖性细胞内pH（pHi）恢复得以证实。在主细胞中鉴定出两种质子转运活性；一种依赖管腔钾离子且对Sch-28080敏感，另一种不依赖管腔钾离子且对管腔巴弗洛霉素A1敏感。因此，OMCDis主细胞同时表达顶端H⁺-K⁺-ATP酶和H⁺-ATP酶活性。闰细胞Na⁺/H⁺交换非依赖性pHi恢复约为主细胞的两倍，且由药理学上相似的机制介导。我们得出以下结论：1）OMCDis主细胞可能在管腔钾离子重吸收和尿液酸化过程中均发挥作用，这与皮质集合管主细胞的作用截然不同；2）OMCDis闰细胞质子转运体在功能上与主细胞相似，这增加了一种类似于主细胞中存在的H⁺-K⁺-ATP酶可能参与闰细胞质子分泌的可能性。
