Wang T, Giebisch G
Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06520, USA.
Am J Physiol. 1996 Jul;271(1 Pt 2):F143-9. doi: 10.1152/ajprenal.1996.271.1.F143.
We have demonstrated in previous studies that luminal administration of low doses of angiotensin II (ANG II) stimulate and high doses of ANG II inhibit fluid and HCO3- transport in proximal tubules of rat kidney. However, the role of ANG II on Na+ and HCO3- transport in the distal nephron has not yet been fully elucidated. The superficial early and late distal tubules (DT) of the nephron segments correspond to the distal convoluted tubule and initial collecting tubule. Accordingly, we investigated the effects of ANG II on Na+, HCO3-, and K+ transport in the early and late DT by separate perfusion of these tubule segments in vivo. [3H]inulin, Na+, K+, and total CO2 concentrations were measured in the perfusate and collected fluid, and transport of sodium (JNa), bicarbonate (JHCO3), potassium (JK), and fluid (JV) were analyzed as an index of the hormone effect. Intravenous infusion of the ANG II receptor antagonist [Sar1,Ile8]ANG II (1 microgram.kg-1.min-1) decreased JV, JNa, and JHCO3 in the early DT and decreased Jv and JNa in the late DT. Addition of ANG II (10(-11) M) to the tubular perfusate significantly increased the Jv, JNa, and JHCO3 in the early DT. Similar studies in late DT demonstrated an increase in Jv and JNa, decrease in JK, but no effect on JHCO3. The effects of ANG II on fluid and ion transport were abolished by the luminal application of amiloride (10(-3) M) and of the angiotensin-receptor blocker [Sar1,Ile8]ANG II (10(-6) M). These results suggest that ANG II stimulates Na+/H+ exchange in the early DT (distal convoluted tubule) and amiloride-sensitive Na+ transport (Na+ channels) in the late DT (initial collecting tubule) of cortical nephrons.
我们在之前的研究中已证明，向大鼠肾近端小管管腔内给予低剂量血管紧张素II（ANG II）会刺激其液体和HCO3-转运，而高剂量ANG II则会抑制这些转运。然而，ANG II在远端肾单位中对Na+和HCO3-转运的作用尚未完全阐明。肾单位节段的浅表早期和晚期远端小管（DT）分别对应于远端曲管和初始集合小管。因此，我们通过在体内分别灌注这些小管节段，研究了ANG II对早期和晚期DT中Na+、HCO3-和K+转运的影响。在灌注液和收集液中测量[3H]菊粉、Na+、K+和总CO2浓度，并分析钠（JNa）、碳酸氢盐（JHCO3）、钾（JK）和液体（JV）的转运情况，以此作为激素作用的指标。静脉输注ANG II受体拮抗剂[Sar1，Ile8]ANG II（1微克·千克-1·分钟-1）会降低早期DT中的JV、JNa和JHCO3，并降低晚期DT中的Jv和JNa。向肾小管灌注液中添加ANG II（10(-11) M）可显著增加早期DT中的Jv、JNa和JHCO3。在晚期DT中进行的类似研究表明Jv和JNa增加，JK降低，但对JHCO3无影响。管腔内应用氨氯地平（10(-3) M）和血管紧张素受体阻滞剂[Sar1，Ile8]ANG II（10(-6) M）可消除ANG II对液体和离子转运的影响。这些结果表明，ANG II刺激皮质肾单位早期DT（远端曲管）中的Na+/H+交换以及晚期DT（初始集合小管）中对氨氯地平敏感的Na+转运（Na+通道）。
