Liu Ruisheng, Ren YiLin, Garvin Jeffrey L, Carretero Oscar A
Division of Hypertension and Vascular Research, Henry Ford Hospital, Detroit, Michigan, USA.
Kidney Int. 2004 Jul;66(1):268-74. doi: 10.1111/j.1523-1755.2004.00727.x.
Superoxide (O(2) (-)) has been shown to augment tubuloglomerular feedback (TGF) both in vivo and in vitro by scavenging nitric oxide (NO) in the macula densa (MD). We hypothesized that in addition to this mechanism O(2) (-) potentiates TGF by acting directly on the afferent arteriole (Af-Art).
Microdissected Af-Arts and adherent tubular segments containing the MD were simultaneously microperfused in vitro, maintaining Af-Art pressure at 60 mm Hg. TGF response was determined by measuring changes in Af-Art diameter while increasing NaCl in the MD perfusate from 11/10 to 81/80 mmol/L Na/Cl.
To determine whether O(2) (-) acts at the MD in the absence of MD NO, we inhibited MD nNOS with 7-nitroindazole (7-NI) and added Tempol to the lumen. When 7-NI was added to the MD lumen, it increased TGF from 2.3 +/- 0.2 to 4.2 +/- 0.2 microm (P < 0.01). When Tempol was added to the MD lumen in the presence of 7-NI, it had no effect on TGF. To investigate whether O(2) (-) has any effect via the Af-Art in the absence of MD NO, we inhibited MD nNOS with 7-NI and added Tempol to the bath to scavenge O(2) (-) in the Af-Art. Adding Tempol to the bath with 7-NI in the MD lumen reduced TGF from 3.9 +/- 0.3 to 2.8 +/- 0.5 microm (P < 0.05 vs. 7-NI). To see if this effect was due to O(2) (-) scavenging NO production by the endothelium, we repeated the experiment in Af-Arts with damaged endothelium and found that adding Tempol to the bath lowered TGF from 3.4 +/- 0.9 to 1.2 +/- 0.6 microm (P < 0.01). When catalase was added to the bath together with Tempol, TGF response was not modified.
We concluded that it is O(2) (-) rather than H(2)O(2) that enhances TGF response, both directly by constricting the Af-Art and indirectly by scavenging NO in the MD.
超氧化物（O₂⁻）已被证明在体内和体外均可通过清除致密斑（MD）中的一氧化氮（NO）来增强肾小管-肾小球反馈（TGF）。我们推测，除了这种机制外，O₂⁻还可通过直接作用于入球小动脉（Af-Art）来增强TGF。
在体外同时对显微解剖的Af-Arts和含有MD的附着肾小管节段进行显微灌注，将Af-Art压力维持在60 mmHg。通过测量Af-Art直径的变化来确定TGF反应，同时将MD灌注液中的NaCl从11/10 mmol/L Na/Cl增加到81/80 mmol/L Na/Cl。
为了确定在MD中不存在NO时O₂⁻是否在MD起作用，我们用7-硝基吲唑（7-NI）抑制MD中的神经元型一氧化氮合酶（nNOS），并向管腔中添加Tempol。当向MD管腔中添加7-NI时，TGF从2.3±0.2微米增加到4.2±0.2微米（P<0.01）。当在存在7-NI的情况下向MD管腔中添加Tempol时，它对TGF没有影响。为了研究在MD中不存在NO时O₂⁻是否通过Af-Art产生任何影响，我们用7-NI抑制MD中的nNOS，并向浴槽中添加Tempol以清除Af-Art中的O₂⁻。在MD管腔中存在7-NI的情况下向浴槽中添加Tempol可使TGF从3.9±0.3微米降低到2.8±0.5微米（与7-NI相比，P<0.05）。为了确定这种作用是否是由于O₂⁻清除了内皮产生的NO，我们在具有受损内皮的Af-Arts中重复了该实验，发现向浴槽中添加Tempol可使TGF从3.4±0.9微米降低到1.2±0.6微米（P<0.01）。当将过氧化氢酶与Tempol一起添加到浴槽中时，TGF反应未改变。
我们得出结论，增强TGF反应的是O₂⁻而非过氧化氢（H₂O₂），其增强方式既有直接收缩Af-Art，也有间接清除MD中的NO。
