Ortiz Pablo A, Garvin Jeffrey L
Division of Hypertension and Vascular Research, Henry Ford Health Sciences Center, Detroit, Michigan 48202, USA.
Am J Physiol Renal Physiol. 2002 Nov;283(5):F957-62. doi: 10.1152/ajprenal.00102.2002.
The thick ascending limb of the loop of Henle (THAL) plays an important role in the regulation of NaCl and water reabsorption. In vivo studies have shown that the free radical superoxide (O) stimulates Na and water reabsorption by the kidney. However, it is not known whether O regulates transport along the nephron in general or in the THAL specifically. We hypothesized that O stimulates THAL NaCl reabsorption. Cl absorption was measured in isolated, perfused THALs from Sprague-Dawley rats. First, we tested whether extracellular O stimulates Cl absorption. Addition of the O-generating system xanthine oxidase/hypoxanthine increased Cl absorption from 112.7 +/- 12.0 to 146.2 +/- 13.9 pmol. mm(-1). min(-1), a 33% increase (P < 0.03). When superoxide dismutase (300 U/ml) was present in the bath, addition of xanthine oxidase/hypoxanthine did not significantly increase Cl absorption (116.9 +/- 13.8 vs. 102.5 +/- 8.5 pmol. mm(-1). min(-1)). Furthermore, adding 200 nM H(2)O(2) to the bath did not significantly affect Cl absorption (from 130.3 +/- 13.7 to 125.3 +/- 19.6 pmol. mm(-1). min(-1)). Because extracellular O stimulated Cl absorption, we next tested whether endogenously produced O could stimulate transport. Under basal conditions, THALs produced detectable amounts of O, as measured by lucigenin-enhanced chemiluminescence. Adding the O scavenger tempol to the bath decreased Cl absorption from 198.1 +/- 35.4 to 132.4 +/- 23.5 pmol. mm(-1). min(-1), a 31% decrease (P < 0.02). To make sure tempol was not exerting cytotoxic effects, we tested whether its effect was reversible. With tempol in the bath, Cl absorption was 117.2 +/- 9.3 pmol. mm(-1). min(-1). Sixty minutes after tempol was removed from the bath, Cl absorption had increased to 149.2 +/- 9.1 pmol. mm(-1). min(-1) (P < 0.05). We concluded that both exogenous and endogenous O stimulate THAL NaCl absorption. To our knowledge, these are the first data showing a direct effect of O on nephron transport.
亨氏袢升支粗段（THAL）在氯化钠和水重吸收的调节中起重要作用。体内研究表明，自由基超氧化物（O）可刺激肾脏对钠和水的重吸收。然而，尚不清楚O是否一般调节沿肾单位的转运，还是特异性调节THAL中的转运。我们推测O可刺激THAL对氯化钠的重吸收。在来自Sprague-Dawley大鼠的分离、灌注的THAL中测量氯的吸收。首先，我们测试细胞外O是否刺激氯的吸收。添加产O系统黄嘌呤氧化酶/次黄嘌呤可使氯的吸收从112.7±12.0增加至146.2±13.9 pmol·mm⁻¹·min⁻¹，增加了33%（P<0.03）。当浴液中存在超氧化物歧化酶（300 U/ml）时，添加黄嘌呤氧化酶/次黄嘌呤并未显著增加氯的吸收（116.9±13.8与102.5±8.5 pmol·mm⁻¹·min⁻¹）。此外，向浴液中添加200 nM过氧化氢对氯的吸收没有显著影响（从130.3±13.7至125.3±19.6 pmol·mm⁻¹·min⁻¹）。由于细胞外O刺激氯的吸收，接下来我们测试内源性产生的O是否能刺激转运。在基础条件下，通过光泽精增强化学发光法测量，THAL产生可检测量的O。向浴液中添加O清除剂tempol可使氯的吸收从198.1±35.4降至132.4±23.5 pmol·mm⁻¹·min⁻¹，降低了31%（P<0.02）。为确保tempol没有发挥细胞毒性作用，我们测试其作用是否可逆。浴液中有tempol时，氯的吸收为117.2±9.3 pmol·mm⁻¹·min⁻¹。从浴液中去除tempol 60分钟后，氯的吸收增加至149.2±9.1 pmol·mm⁻¹·min⁻¹（P<0.05）。我们得出结论，外源性和内源性O均刺激THAL对氯化钠的吸收。据我们所知，这些是显示O对肾单位转运有直接作用的首批数据。
