Ismailov I I, Awayda M S, Jovov B, Berdiev B K, Fuller C M, Dedman J R, Kaetzel M, Benos D J
Department of Physiology and Biophysics, University of Alabama at Birmingham, 35294-0005, USA.
J Biol Chem. 1996 Mar 1;271(9):4725-32. doi: 10.1074/jbc.271.9.4725.
Cystic fibrosis airway epithelia exhibit enhanced Na+ reabsorption in parallel with diminished Cl- secretion. We tested the hypothesis that the cystic fibrosis transmembrane conductance regulator (CFTR) directly affects epithelial Na+ channel activity by co-incorporating into planar lipid bilayers immunopurified bovine tracheal CFTR and either heterologously expressed rat epithelial Na+ channel ( alpha,b eta,gamma-rENaC) or an immunopurified bovine renal Na+ channel protein complex. The single channel open probability (Po) of rENaC was decreased by 24% in the presence of CFTR. Protein kinase A (PKA) plus ATP activated CFTR, but did not have any effect on rENaC. CFTR also decreased the extent of elevation of the renal Na+ channel Po following PKA-mediated phosphorylation. Moreover, the presence of CFTR prohibited the inward rectification of the gating of this renal Na+ channel normally induced by PKA-mediated phosphorylation, thus down-regulating inward Na+ current. This interaction between CFTR and Na+ channels occurs independently of whether or not wild-type CFTR is conducting anions. However, the nonconductive CFTR mutant, G551D CFTR, cannot substitute for the wild-type molecule. Our results indicate that CFTR can directly down-regulate single Na+ channel activity, thus accounting, at least in part, for the observed differences in Na+ transport between normal and cystic fibrosis-affected airway epithelia.
囊性纤维化气道上皮细胞表现出增强的Na⁺重吸收，同时Cl⁻分泌减少。我们检验了这样一个假说，即囊性纤维化跨膜传导调节因子（CFTR）通过将免疫纯化的牛气管CFTR与异源表达的大鼠上皮Na⁺通道（α、β、γ-rENaC）或免疫纯化的牛肾Na⁺通道蛋白复合物共掺入平面脂质双分子层，直接影响上皮Na⁺通道活性。在存在CFTR的情况下，rENaC的单通道开放概率（Po）降低了24%。蛋白激酶A（PKA）加ATP激活了CFTR，但对rENaC没有任何影响。CFTR也降低了PKA介导的磷酸化后肾Na⁺通道Po升高的程度。此外，CFTR的存在阻止了通常由PKA介导的磷酸化诱导的该肾Na⁺通道门控的内向整流，从而下调内向Na⁺电流。CFTR与Na⁺通道之间的这种相互作用独立于野生型CFTR是否在传导阴离子而发生。然而，非传导性CFTR突变体G551D CFTR不能替代野生型分子。我们的结果表明，CFTR可以直接下调单个Na⁺通道活性，从而至少部分地解释了正常气道上皮细胞和受囊性纤维化影响的气道上皮细胞之间观察到的Na⁺转运差异。
