Cantiello H F, Scott J A, Rabito C A
Am J Physiol. 1987 Apr;252(4 Pt 2):F590-7. doi: 10.1152/ajprenal.1987.252.4.F590.
Na+ influx and efflux from confluent monolayers of an epithelial cell line with multiple differentiated characteristics of the straight segment of the renal proximal tubule were studied in the presence and absence of a pH gradient. The results show that Na+ influx in the absence of a pH gradient is inhibited by amiloride as well as by complete replacement of Cl- by an impermeable anion, such as isethionate. Dissipation of cell membrane potential by increasing the potassium concentration of the extracellular medium in the presence of valinomycin also inhibited Na+ influx, whereas sodium influx induced by an H+ gradient was not affected. Inhibition of Na+ influx by different maneuvers produced hyperpolarization of the plasma cell membrane, as would be expected if the sodium movement involved net displacement of charges. Calcium and other divalent and trivalent cations also inhibited Na+ influx measured in the absence of an H+ gradient. Na+ influx induced by a pH gradient, however, was not affected. Like the Na+-H+-exchange system, the conductive Na+ pathway is localized in the apical membrane of the epithelial cells. From these results, we conclude that at least a fraction of transepithelial Na+ transport in LLC-PK1 monolayers occurs through a simple rheogenic transport system.
在有和没有pH梯度的情况下，研究了具有肾近端小管直段多种分化特征的上皮细胞系汇合单层中Na⁺的流入和流出。结果表明，在没有pH梯度的情况下，氨氯吡咪以及用不可渗透的阴离子（如羟乙磺酸盐）完全替代Cl⁻可抑制Na⁺流入。在缬氨霉素存在下，通过增加细胞外培养基中的钾浓度来消散细胞膜电位也抑制了Na⁺流入，而由H⁺梯度诱导的钠流入则不受影响。通过不同操作抑制Na⁺流入会导致质膜超极化，这正如如果钠的移动涉及净电荷位移所预期的那样。钙以及其他二价和三价阳离子也抑制了在没有H⁺梯度时测量的Na⁺流入。然而，由pH梯度诱导的Na⁺流入不受影响。与Na⁺-H⁺交换系统一样，传导性Na⁺途径定位于上皮细胞的顶端膜。从这些结果中，我们得出结论，LLC-PK1单层中的跨上皮Na⁺转运至少有一部分是通过简单的生电转运系统进行的。
