Lu M, Wang W H
Department of Pharmacology, New York Medical College, Valhalla, New York 10595, USA.
Am J Physiol. 1998 Jul;275(1):C309-16. doi: 10.1152/ajpcell.1998.275.1.C309.
We previously demonstrated that nitric oxide (NO) stimulates the basolateral small-conductance K+ channel (SK) via a cGMP-dependent pathway [M. Lu and W. H. Wang. Am. J. Physiol. 270 (Cell Physiol. 39): C1336-C1342, 1996]. Because NO at high concentration has been shown to react with superoxide (O-2) to form peroxynitrite (OONO-) [W. A. Pryor and G. L. Squadrito. Am. J. Physiol. 268 (Lung Cell. Mol. Physiol. 12): L699-L722, 1995 and M. S. Wolin. Microcirculation 3: 1-17, 1996], we extended our study to examine, using patch-clamp technique, the effect of high concentrations of NO on SK in cortical collecting duct (CCD) of rat kidney. Addition of NO donors [100-200 microM S-nitroso-N-acetyl-penicillamine (SNAP) or sodium nitroprusside (SNP)] reduced channel activity, defined as the product of channel number and open probability, to 15 and 25% of the control value, respectively. The inhibitory effect of NO was completely abolished in the presence of 10 mM Tiron, an intracellular scavenger of O-2. NO donors, 10 microM SNAP or SNP, which stimulate channel activity under control conditions, can also inhibit SK in the presence of an O-2 donor, pyrogallol, or in the presence of an inhibitor of superoxide dismutase, diethyldithiocarbamic acid. The inhibitory effect of NO is still observed in the presence of exogenous cGMP, suggesting that the NO-induced inhibition is not the result of decreased cGMP production. We conclude that the inhibitory effect of NO on channel activity results from an interaction between NO and O-2.
我们先前证明，一氧化氮（NO）通过环磷酸鸟苷（cGMP）依赖途径刺激基底外侧小电导钾通道（SK）[M. 卢和W. H. 王。《美国生理学杂志》270（细胞生理学39）：C1336 - C1342，1996]。由于高浓度的NO已被证明可与超氧阴离子（O₂⁻）反应形成过氧亚硝酸根（OONO⁻）[W. A. 普赖尔和G. L. 斯夸德里托。《美国生理学杂志》268（肺细胞与分子生理学12）：L699 - L722，1995以及M. S. 沃林。《微循环》3：1 - 17，1996]，我们扩展了研究，采用膜片钳技术，研究高浓度NO对大鼠肾皮质集合管（CCD）中SK的影响。添加NO供体[100 - 200微摩尔S - 亚硝基 - N - 乙酰青霉胺（SNAP）或硝普钠（SNP）]分别将通道活性（定义为通道数量与开放概率的乘积）降低至对照值的15%和25%。在存在10毫摩尔替洛隆（一种细胞内O₂⁻清除剂）的情况下，NO的抑制作用完全消除。在对照条件下刺激通道活性的10微摩尔SNAP或SNP等NO供体，在存在O₂供体邻苯三酚或超氧化物歧化酶抑制剂二乙基二硫代氨基甲酸的情况下，也能抑制SK。在外源cGMP存在的情况下，仍可观察到NO的抑制作用，这表明NO诱导的抑制不是cGMP生成减少的结果。我们得出结论，NO对通道活性的抑制作用源于NO与O₂⁻之间的相互作用。
