Siebens A W, Boron W F
Department of Physiology, Yale University School of Medicine, New Haven, Connecticut 06510.
Am J Physiol. 1989 Feb;256(2 Pt 2):F342-53. doi: 10.1152/ajprenal.1989.256.2.F342.
We used intracellular pH-sensitive and voltage microelectrodes to examine the effects of depolarization on intracellular pH (pHi) in isolated perfused proximal tubules from the tiger salamander Ambystoma tigrinum. Tubules were depolarized by raising [K+] in the bath (b) or lumen (l), or by adding Ba2+ (1 mM) to the bath or lumen, always in nominally HCO3-free solutions. Increasing [K+]b from 2.5 to 50 mM caused the basolateral membrane to depolarize by an average of 45 mV, and pHi to increase by 0.23 over 3 min. Similar alkalinization was observed when basolateral Ba2+ (1 mM) was used to depolarize the cell at constant extracellular [K+], suggesting that the alkalinization observed during exposure to elevated [K+]b results from depolarization rather than an increase in [K+]b. The initial rate of depolarization-induced alkalinization (DIA) was proportional to the magnitude of the depolarization, regardless of whether tubules were depolarized by elevated [K+]b, elevated [K+]l, or by basolateral Ba2+. An exception was the initial rate of the alkalinization caused by 1 mM luminal Ba2+, which was more than 10-fold greater than that predicted from the depolarization. The voltage and pHi responses to basolateral Ba2+ were smaller in some tubules than others, as were the responses to elevated [K+]l. Tubules with small responses to 1 mM [Ba2+]b had large responses to 50 mM [K+]l, whereas tubules with large responses to 1 mM [Ba2+]b had small responses to 50 mM [K+]l. This variability can be accounted for by differences in the luminal K+ conductance. The DIA was partially inhibited by removal of Na+ from only the lumen or only the bath, but completely inhibited by bilateral Na+ removal. We conclude that the depolarization-induced alkalinization results from additive effects of Na+-dependent processes at both the luminal and basolateral membranes.
我们使用细胞内pH敏感微电极和电压微电极，来研究去极化对虎螈（Ambystoma tigrinum）离体灌注近端小管细胞内pH（pHi）的影响。通过提高浴液（b）或管腔（l）中的[K+]，或向浴液或管腔中添加Ba2+（1 mM）使小管去极化，实验始终在名义上无HCO3的溶液中进行。将[K+]b从2.5 mM提高到50 mM会使基底外侧膜平均去极化45 mV，并且pHi在3分钟内升高0.23。当在细胞外[K+]恒定的情况下，使用基底外侧Ba2+（1 mM）使细胞去极化时，也观察到了类似的碱化现象，这表明在暴露于升高的[K+]b期间观察到的碱化是由去极化引起的，而不是[K+]b的增加。去极化诱导的碱化（DIA）的初始速率与去极化的幅度成正比，无论小管是通过升高[K+]b、升高[K+]l还是通过基底外侧Ba2+去极化。一个例外是由1 mM管腔Ba2+引起的碱化的初始速率，它比根据去极化预测的值大10倍以上。对基底外侧Ba2+的电压和pHi反应在一些小管中比其他小管小，对升高的[K+]l的反应也是如此。对1 mM [Ba2+]b反应小的小管对50 mM [K+]l反应大，而对1 mM [Ba2+]b反应大的小管对50 mM [K+]l反应小。这种变异性可以通过管腔K+电导的差异来解释。仅从管腔或仅从浴液中去除Na+会部分抑制DIA，但双侧去除Na+会完全抑制DIA。我们得出结论，去极化诱导的碱化是由管腔和基底外侧膜上Na+依赖性过程的累加效应引起的。
