Konieczkowski M, Dunn M J
Department of Medicine, Case Western Reserve University, Cleveland, Ohio 44106.
J Cell Physiol. 1988 May;135(2):235-43. doi: 10.1002/jcp.1041350210.
Sodium transport in the papillary collecting duct (PCD) is poorly understood because of the inaccessibility of the distal nephron to micropuncture. Cultured rat renal papillary collecting tubule (RPCT) cells were investigated as a model for the PCD. RPCT cells have the morphologic appearance and hormonal responsiveness of the papillary collecting tubule. Sodium transport was studied using 22Na+ uptake measurements. Sodium uptake, measured at 23 degrees C in the absence of K+ and in the presence of 0.5 mM ouabain, was saturable at 100 mM extracellular NaCl, and half-maximal uptake occurred at 40 mM NaCl. The accumulation of 22Na+ appeared to be intracellular and was regulated by (Na+,K+)-ATPase activity, since activation of the Na+/K+ pump with K+ reduced 22Na+ accumulation by 90%. The time course for uptake was linear, showed only a single component, and followed first order kinetics with a t1/2 of 16 min. Amiloride and lithium inhibited 22Na+ influx, and a Dixon plot was linear, with a Ki of 16 microM amiloride. Chloride replacement of 1 mM furosemide, with or without K+, reduced uptake by only 20%. Sodium efflux from RPCT cells in the presence of ouabain showed a similar time course (t1/2, 15 min) and was also inhibited by amiloride (IC50 = 20 microM). Increased extracellular pH stimulated 22Na+ uptake and inhibited 22Na+ efflux. Addition of permeable organic acids, acetate, and bicarbonate, enhanced 22Na+ uptake. These results are consistent with Na+/H+ and Na+/Na+ exchange as mechanisms of 22Na+ uptake in the RPCT cell. This exchanger may be important in regulation of transepithelial sodium flux, maintenance of intracellular pH and cell volume, and hormonal stimulation of the papillary collecting duct.
由于远端肾单位难以进行微穿刺，对乳头集合管（PCD）中的钠转运了解甚少。培养的大鼠肾乳头集合小管（RPCT）细胞被作为PCD的模型进行研究。RPCT细胞具有乳头集合小管的形态外观和激素反应性。使用22Na+摄取测量来研究钠转运。在23摄氏度、无钾且存在0.5 mM哇巴因的条件下测量的钠摄取，在细胞外NaCl浓度为100 mM时达到饱和，半数最大摄取发生在40 mM NaCl时。22Na+的积累似乎是细胞内的，并且受（Na+，K+）-ATP酶活性调节，因为用钾激活Na+/K+泵可使22Na+积累减少90%。摄取的时间进程是线性的，仅显示一个成分，并遵循一级动力学，t1/2为16分钟。氨氯吡咪和锂抑制22Na+内流，Dixon图呈线性，氨氯吡咪的Ki为16 microM。用1 mM呋塞米替代氯离子，无论有无钾，摄取仅减少20%。在存在哇巴因的情况下，RPCT细胞的钠外流显示出相似的时间进程（t1/2，15分钟），并且也受到氨氯吡咪的抑制（IC50 = 20 microM）。细胞外pH升高刺激22Na+摄取并抑制22Na+外流。添加可渗透的有机酸、乙酸盐和碳酸氢盐可增强22Na+摄取。这些结果与Na+/H+和Na+/Na+交换作为RPCT细胞中22Na+摄取机制一致。这种交换体可能在调节跨上皮钠通量、维持细胞内pH和细胞体积以及乳头集合管的激素刺激中起重要作用。
