Monzon Casandra M, Garvin Jeffrey L
From the Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, OH.
Hypertension. 2015 Jun;65(6):1245-50. doi: 10.1161/HYPERTENSIONAHA.115.05356. Epub 2015 Apr 20.
Thick ascending limbs reabsorb 25% to 30% of the filtered NaCl. About 50% to 70% is reabsorbed via the transcellular pathway and 30% to 50% is reabsorbed through the Na-selective paracellular pathway. Nitric oxide (NO) inhibits transepithelial Na reabsorption, but its effects on the paracellular pathway are unknown. We hypothesized that NO decreases the selectivity of the paracellular pathway in thick ascending limbs via cGMP-dependent protein kinase. To assess relative Na/Cl permeability ratios (PNa/PCl), we perfused rat thick ascending limbs and measured the effect of reducing bath NaCl on transepithelial voltage, creating dilution potentials, with vehicle, NO donors, and endogenous NO. PNa/PCl was calculated using the Goldman-Hodgkin-Katz equation. Reducing bath Na/Cl to 16/8, 32/24, and 64/56 mmol/L created dilution potentials of -13.6±2.2, -10.8±3.0, and -6.1±0.9 mV, respectively. Calculated PNa/PCls were 2.0±0.2, 2.2±0.5, and 1.9±0.2. The NO donor spermine NONOate (200 µmol/L) blunted the dilution potential caused by 32/24 mmol/L Na/Cl from -11.1±2.1 to -6.5±1.6 mV (P<0.004) and PNa/PCl from 2.2±0.4 to 1.5±0.2. Nitroglycerin (200 µmol/L), another NO donor, also reduced PNa/PCl. Controls showed no significant changes. Dibutyryl-cGMP decreased dilution potentials from -13.4±2.9 to -7.5±1.8 mV (n=6; P<0.01). cGMP-dependent protein kinase inhibition with KT5823 (4 µmol/L) blocked the effect of spermine NONOate, whereas phosphodiesterase 2 inhibition did not. Endogenously produced NO mimicked the effect of the NO donors. In conclusion, NO reduces the selectivity of the paracellular pathway in thick ascending limbs via cGMP and cGMP-dependent protein kinase.
髓袢升支粗段重吸收25%至30%的滤过氯化钠。约50%至70%通过跨细胞途径重吸收，30%至50%通过钠选择性细胞旁途径重吸收。一氧化氮（NO）抑制上皮细胞钠重吸收，但其对细胞旁途径的影响尚不清楚。我们推测NO通过环磷酸鸟苷（cGMP）依赖性蛋白激酶降低髓袢升支粗段细胞旁途径的选择性。为评估相对钠/氯通透性比值（PNa/PCl），我们灌注大鼠髓袢升支粗段，并测量降低浴液中氯化钠对跨上皮电压的影响，利用载体、NO供体和内源性NO产生稀释电位。使用戈德曼-霍奇金-卡茨方程计算PNa/PCl。将浴液中钠/氯降至16/8、32/24和64/56 mmol/L分别产生-13.6±2.2、-10.8±3.0和-6.1±0.9 mV的稀释电位。计算得到的PNa/PCl分别为2.0±0.2、2.2±0.5和1.9±0.2。NO供体精胺NONOate（200 µmol/L）使由32/24 mmol/L钠/氯引起的稀释电位从-11.1±2.1 mV降至-6.5±1.6 mV（P<0.004），PNa/PCl从2.2±0.4降至1.5±0.2。另一种NO供体硝酸甘油（200 µmol/L）也降低了PNa/PCl。对照组无显著变化。二丁酰-cGMP使稀释电位从-13.4±2.9 mV降至-7.5±1.8 mV（n = 6；P<0.01）。用KT5823（4 µmol/L）抑制cGMP依赖性蛋白激酶可阻断精胺NONOate的作用，而抑制磷酸二酯酶2则无此作用。内源性产生的NO模拟了NO供体的作用。总之，NO通过cGMP和cGMP依赖性蛋白激酶降低髓袢升支粗段细胞旁途径的选择性。
