Friedman P A, Andreoli T E
J Gen Physiol. 1982 Nov;80(5):683-711. doi: 10.1085/jgp.80.5.683.
These experiments evaluated salt transport processes in isolated cortical thick limbs of Henle (cTALH) obtained from mouse kidney. When the external solutions consisted of Krebs-Ringer bicarbonate (KRB), pH 7.4, and a 95% O2-5% CO2 gas phase, the spontaneous transepithelial voltage (Ve, mV, lumen-to-bath) was approximately mV; the net rate of Cl- absorption (JnetCl) was approximately 3,600 pmols s-1 cm-2; the net rate of osmotic solute absorption Jnetosm was twice JnetCl; and the net rate of total CO2 transport (JnetCO2) was indistinguishable from zero. Thus, net Cl- absorption was accompanied by the net absorption of a monovalent cation, presumably Na+, and net HCO3- absorption was negligible. This salt transport process was stimulated by (CO2 + HCO3-): omission of CO2 from the gas phase and HCO3- from external solutions reduced JnetCl, Jnetosm, and Ve by 50%. Furthermore, 10(-4) M luminal furosemide abolished JnetCl and Ve entirely. The lipophilic carbonic anhydrase inhibitor ethoxzolamide (10(-4) M, either luminal or peritubular) inhibited (CO2 + HCO3-)-stimulated JnetCl, Jnetosm, and Ve by approximately 50%; however, when the combination (CO2 + HCO3-) was absent, ethoxzolamide had no detectable effect on salt transport. Ve was reduced or abolished entirely by omission of either Na+ or Cl- from external solutions, by peritubular K+ removal, by 10(-3) M peritubular ouabain, and by 10(-4) M luminal SITS. However, Ve was unaffected by 10(-3) M peritubular SITS, or by the hydrophilic carbonic anhydrase inhibitor acetazolamide (2.2 x 10(-4) M, lumen plus bath). We interpret these data to indicate that (CO2 + HCO3-)-stimulated NaCl absorption in the cTALH involved two synchronous apical membrane antiport processes: one exchanging luminal Na+ for cellular H+; and the other exchanging luminal Cl- for cellular HCO3- or OH-, operating in parallel with a (CO2+ HCO3-)-independent apical membrane NaCl cotransport mechanism.
这些实验评估了从小鼠肾脏获取的离体亨氏袢皮质厚升支（cTALH）中的盐转运过程。当外部溶液由pH 7.4的 Krebs - Ringer碳酸氢盐（KRB）和95% O₂ - 5% CO₂气相组成时，自发跨上皮电压（Ve，mV，管腔到浴液）约为 mV；Cl⁻吸收的净速率（JnetCl）约为3600 pmol·s⁻¹·cm⁻²；渗透溶质吸收的净速率Jnetosm是JnetCl的两倍；总CO₂转运的净速率（JnetCO₂）与零无显著差异。因此，Cl⁻的净吸收伴随着单价阳离子（可能是Na⁺）的净吸收，而HCO₃⁻的净吸收可忽略不计。这种盐转运过程受到（CO₂ + HCO₃⁻）的刺激：气相中去除CO₂以及外部溶液中去除HCO₃⁻会使JnetCl、Jnetosm和Ve降低50%。此外，10⁻⁴ M管腔呋塞米完全消除了JnetCl和Ve。亲脂性碳酸酐酶抑制剂乙氧唑胺（10⁻⁴ M，管腔或肾小管周围）使（CO₂ + HCO₃⁻）刺激的JnetCl、Jnetosm和Ve降低约50%；然而，当不存在（CO₂ + HCO₃⁻）组合时，乙氧唑胺对盐转运没有可检测到的影响。通过从外部溶液中去除Na⁺或Cl⁻、去除肾小管周围的K⁺、10⁻³ M肾小管周围哇巴因以及10⁻⁴ M管腔SITS，Ve会降低或完全消除。然而，Ve不受10⁻³ M肾小管周围SITS或亲水性碳酸酐酶抑制剂乙酰唑胺（管腔加浴液中2.2×10⁻⁴ M）的影响。我们对这些数据的解释是，cTALH中（CO₂ + HCO₃⁻）刺激的NaCl吸收涉及两个同步的顶端膜反向转运过程：一个是将管腔中的Na⁺与细胞内的H⁺交换；另一个是将管腔中的Cl⁻与细胞内的HCO₃⁻或OH⁻交换，与一个不依赖（CO₂ + HCO₃⁻）的顶端膜NaCl共转运机制并行运作。
