兔S3近端小管中的细胞内pH调节：基底外侧Cl-HCO3交换和Na-HCO3共转运

Intracellular pH regulation in rabbit S3 proximal tubule: basolateral Cl-HCO3 exchange and Na-HCO3 cotransport.

作者信息

Nakhoul N L, Chen L K, Boron W F

机构信息

Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06510.

出版信息

Am J Physiol. 1990 Feb;258(2 Pt 2):F371-81. doi: 10.1152/ajprenal.1990.258.2.F371.

DOI:10.1152/ajprenal.1990.258.2.F371

PMID:2155541

Abstract

We studied the role of basolateral HCO3- transport in the regulation of intracellular pH (pHi) in the isolated perfused S3 segment of the rabbit proximal tubule. pHi was calculated from absorbance spectra of the pH-sensitive dye dimethylcarboxyfluorescein. Solutions were normally buffered to pH 7.4 at 37 degrees C with 25 mM HCO3- 5% CO2. pHi fell by approximately 0.17 when luminal [HCO3-] was lowered to 5 mM at fixed PCO2 (i.e., reducing pH to 6.8) but by approximately 0.42 when [HCO3-] in the bath (i.e., basolateral solution) was lowered to 5 mM. The pHi decrease elicited by reducing bath [HCO3-] was substantially reduced by removal of Cl- or Na+, suggesting that components of basolateral HCO3- transport are Cl- and/or Na+ dependent. We tested for the presence of basolateral Cl-HCO3 exchange by removing bath Cl-. This caused pHi to increase by approximately 0.23, with an initial rate of approximately 100 X 10(-4) pH/s. Although the initial rate of this pHi increase was not reduced by removing Na+ bilaterally, it was substantially lowered by the nominal removal of HCO3- from bath and lumen or by the addition of 0.1 mM 4,4'-diisothiocyanostilbene-2,2'-disulfonate (DIDS) to the bath. The results thus suggest that a Na-independent Cl-HCO3 exchanger is present at the basolateral membrane. We tested for the presence of basolateral Na-HCO3 cotransport by removing bath Na+. This caused pHi to fall reversibly by approximately 0.26 with initial rates of pHi decline and recovery being approximately 30 and approximately 41 X 10(-4) pH/s, respectively. Although the bilateral removal of Cl- had no effect on these rates, the nominal removal of HCO3- or the presence of DIDS substantially slowed the pHi changes. Thus, in addition to a Cl-HCO3 exchanger, the basolateral membrane of the S3 proximal tubule also appears to possess a Na-HCO3 cotransport mechanism. The data do not rule out the possibility of other basolateral HCO3- transporters.

摘要

我们研究了基底外侧HCO₃⁻转运在兔近端小管分离灌注S3段细胞内pH（pHi）调节中的作用。pHi通过pH敏感染料二甲基羧基荧光素的吸收光谱计算得出。溶液通常在37℃下用25 mM HCO₃⁻、5% CO₂缓冲至pH 7.4。当管腔[HCO₃⁻]在固定PCO₂下降至5 mM（即pH降至6.8）时，pHi下降约0.17，但当浴液（即基底外侧溶液）中的[HCO₃⁻]降至5 mM时，pHi下降约0.42。通过去除Cl⁻或Na⁺，降低浴液[HCO₃⁻]引起的pHi下降显著减少，这表明基底外侧HCO₃⁻转运的成分是Cl⁻和/或Na⁺依赖性的。我们通过去除浴液中的Cl⁻来测试基底外侧Cl⁻-HCO₃⁻交换的存在。这导致pHi增加约0.23，初始速率约为100×10⁻⁴pH/s。虽然通过双侧去除Na⁺并没有降低这种pHi增加的初始速率，但通过从浴液和管腔中名义上去除HCO₃⁻或在浴液中添加0.1 mM 4,4'-二异硫氰基芪-2,2'-二磺酸盐（DIDS），该速率显著降低。因此，结果表明在基底外侧膜存在一种不依赖Na⁺的Cl⁻-HCO₃⁻交换体。我们通过去除浴液中的Na⁺来测试基底外侧Na⁺-HCO₃⁻共转运的存在。这导致pHi可逆地下降约0.26，pHi下降和恢复的初始速率分别约为30和41×10⁻⁴pH/s。虽然双侧去除Cl⁻对这些速率没有影响，但名义上去除HCO₃⁻或存在DIDS会显著减缓pHi的变化。因此，除了Cl⁻-HCO₃⁻交换体外，S3近端小管的基底外侧膜似乎还具有Na⁺-HCO₃⁻共转运机制。这些数据并不排除存在其他基底外侧HCO₃⁻转运体的可能性。