Kurtz I
Department of Medicine, University of California at Los Angeles School of Medicine 90024.
J Clin Invest. 1987 Oct;80(4):928-35. doi: 10.1172/JCI113184.
The apical transport processes responsible for proton secretion were studied in the isolated perfused rabbit S3 proximal tubule. Intracellular pH (pHi) was measured with the pH dye, 2',7'-bis(carboxyethyl)-5,6-carboxyfluorescein. Steady state pHi in S3 tubules in nominally HCO3(-)-free solutions was 7.08 +/- 0.03. Removal of Na+ (lumen) caused a decrease in pHi of 0.34 +/- 0.06 pH/min. The decrease in pHi was inhibited 62% by 1 mM amiloride (lumen) and was unaffected by 50 microM 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (lumen) and Cl- removal (lumen, bath). After a brief exposure to 20 mM NH4Cl, pHi fell by approximately 0.7 and recovered at a rate of 0.89 +/- 0.15 pH/min in the nominal absence of Na+, HCO3-, organic anions, and SO4(2-) (lumen, bath). 1 mM N,N'-dicyclohexylcarbodiimide (lumen), 1 mM N-ethylmaleimide (lumen), 0.5 mM colchicine (bath), and 0.5 mM iodoacetic acid (lumen, bath) inhibited the Na+-independent pHi recovery rate by 73%, 55%, 77%, and 86%, respectively, whereas 1 mM KCN (lumen, bath) did not inhibit pHi recovery. Reduction of intracellular, but not extracellular chloride, also decreased the Na+-independent pHi recovery rate. In conclusion, the S3 proximal tubule has an apical Na+/H+ antiporter with a Michaelis constant for Na+ of 29 mM and a maximum velocity of 0.47 pH/min. S3 tubules also possess a plasma membrane H+-ATPase that can regulate pHi, has a requirement for intracellular chloride, and utilizes ATP derived primarily from glycolysis.
在分离灌注的兔S3近端小管中研究了负责质子分泌的顶端转运过程。用pH染料2',7'-双（羧乙基）-5,6-羧基荧光素测量细胞内pH（pHi）。在名义上不含HCO3(-)的溶液中，S3小管中的稳态pHi为7.08±0.03。去除Na+（管腔）导致pHi以0.34±0.06 pH/分钟的速度下降。1 mM氨氯吡咪（管腔）可抑制pHi下降62%，而50 μM 4,4'-二异硫氰基芪-2,2'-二磺酸（管腔）和去除Cl-（管腔、浴槽）对其无影响。短暂暴露于20 mM NH4Cl后，在名义上不存在Na+、HCO3-、有机阴离子和SO4(2-)（管腔、浴槽）的情况下，pHi下降约0.7，并以0.89±0.15 pH/分钟的速度恢复。1 mM N,N'-二环己基碳二亚胺（管腔）、1 mM N-乙基马来酰亚胺（管腔）、0.5 mM秋水仙碱（浴槽）和0.5 mM碘乙酸（管腔、浴槽）分别抑制不依赖Na+的pHi恢复率73%、55%、77%和86%，而1 mM KCN（管腔、浴槽）不抑制pHi恢复。降低细胞内而非细胞外的氯离子也会降低不依赖Na+的pHi恢复率。总之，S3近端小管具有顶端Na+/H+反向转运体，其对Na+的米氏常数为29 mM，最大速度为0.47 pH/分钟。S3小管还具有一种质膜H+-ATP酶，该酶可调节pHi，需要细胞内氯离子，并利用主要来自糖酵解的ATP。
