Nakhoul N L, Boron W F
Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06510.
J Gen Physiol. 1988 Sep;92(3):395-412. doi: 10.1085/jgp.92.3.395.
We monitored intracellular pH (pHi) in isolated perfused S3 segments of the rabbit proximal tubule, and studied the effect of acetate (Ac-) transport on pHi. pHi was calculated from the absorbance spectrum of 4',5'-dimethyl-5-(and 6) carboxyfluorescein trapped intracellularly. All solutions were nominally HCO3(-)-free. Removal of 10 mM Ac- from bath and lumen caused pHi to rapidly rise by approximately 0.2, and then to decline more slowly to a value approximately 0.35 below the initial one. Removal of only luminal Ac- caused pHi changes very similar to those resulting from bilateral removal of Ac-. When Ac- was removed from bath only, pHi rose rapidly at first, and then continued to rise more slowly. Readdition of Ac- to bath caused pHi to rapidly fall to a value slightly higher than the one prevailing before the removal of Ac- from the bath. In experiments in which Ac- was first removed from both bath and lumen, readdition of 10 mM Ac- to only lumen caused a rapid but small acidification, followed by a slower alkalinization that brought the pHi near the value that prevailed before the bilateral removal of Ac-. The alkalinizing effects caused by the readdition of 10 or 0.5 mM Ac- were indistinguishable. When Ac- was returned to only lumen in the absence of luminal Na+, there was a small and rapid pHi decrease, but no pHi recovery. Removal of Na+ from bath did not affect the pHi transients caused by the addition of Ac- to lumen. In experiments in which Ac- was first removed bilaterally, readdition of Ac- to only bath caused a large and sustained drop in pHi, whereas the subsequent removal of Ac- from the bath caused a slight alkalinization. These pHi changes caused by readdition or removal of Ac- from baths were unaffected by the absence of external Na+. We conclude that there is a Na+/Ac- cotransporter at the luminal membrane, and pathways for acetic acid transport at both luminal and basolateral membranes. The net effect of Ac- transport on pHi is to alkalinize the cell as a result of the luminal entry of Na+/Ac-, which is followed by the luminal and basolateral exit of acetic acid.
我们监测了兔近端小管分离灌注的S3段细胞内pH值（pHi），并研究了醋酸根（Ac-）转运对pHi的影响。pHi是根据细胞内捕获的4',5'-二甲基-5-（和6）羧基荧光素的吸收光谱计算得出的。所有溶液名义上均不含HCO3(-)。从浴液和管腔中去除10 mM Ac-会导致pHi迅速升高约0.2，然后更缓慢地下降至比初始值低约0.35的值。仅去除管腔内的Ac-导致的pHi变化与双侧去除Ac-导致的变化非常相似。当仅从浴液中去除Ac-时，pHi起初迅速升高，然后继续更缓慢地升高。向浴液中重新添加Ac-会使pHi迅速下降至略高于从浴液中去除Ac-之前的值。在浴液和管腔中的Ac-均首先被去除的实验中，仅向管腔中重新添加10 mM Ac-会导致迅速但较小的酸化，随后是较慢的碱化，使pHi接近双侧去除Ac-之前的水平。重新添加10 mM或0.5 mM Ac-引起的碱化作用没有区别。当在没有管腔Na+的情况下仅向管腔中重新添加Ac-时，pHi会有小幅度的快速下降，但不会恢复到初始值。从浴液中去除Na+不会影响向管腔中添加Ac-引起的pHi瞬变。在双侧首先去除Ac-的实验中，仅向浴液中重新添加Ac-会导致pHi大幅持续下降，而随后从浴液中去除Ac-会导致轻微碱化。这些由向浴液中重新添加或去除Ac-引起的pHi变化不受外部Na+缺失的影响。我们得出结论，在管腔膜存在Na+/Ac-共转运体，并且在管腔膜和基底外侧膜都存在醋酸转运途径。Ac-转运对pHi的净效应是使细胞碱化，这是由于Na+/Ac-进入管腔，随后醋酸从管腔和基底外侧排出。
