VanLandingham Lauren G, Gannon Kimberly P, Drummond Heather A
Dept. of Physiology and Biophysics, Univ. of Mississippi Medical Center, 2500 North State St., Jackson, MS 39216-4505, USA.
Am J Physiol Regul Integr Comp Physiol. 2009 Sep;297(3):R723-8. doi: 10.1152/ajpregu.00212.2009. Epub 2009 Jun 24.
Recent studies suggest certain epithelial Na(+) channel (ENaC) proteins may be components of mechanosensitive ion channel complexes in vascular smooth muscle cells that contribute to pressure-induced constriction in middle cerebral arteries (MCA). However, the role of a specific ENaC protein, betaENaC, in pressure-induced constriction of MCAs has not been determined. The goal of this study was to determine whether pressure-induced constriction in the MCA is altered in a mouse model with reduced levels of betaENaC. Using quantitative immunofluorescence, we found whole cell betaENaC labeling in cerebral vascular smooth muscle cells (VSMCs) was suppressed 46% in betaENaC homozygous mutant (m/m) mice compared with wild-type littermates (+/+). MCAs from betaENaC +/+ and m/m mice were isolated and placed in a vessel chamber for myographic analysis. Arteries from betaENaC+/+ mice constricted to stepwise increases in perfusion pressure and developed maximal tone of 10 +/- 2% at 90 mmHg (n = 5). In contrast, MCAs from betaENaC m/m mice developed significantly less tone (4 +/- 1% at 90 mmHg, n = 5). Vasoconstrictor responses to KCl (4-80 mM) were identical between genotypes and responses to phenylephrine (10(-7)-10(-4) M) were marginally altered, suggesting that reduced levels of VSMC betaENaC specifically inhibit pressure-induced constriction. Our findings indicate betaENaC is required for normal pressure-induced constriction in the MCA and provide further support for the hypothesis that betaENaC proteins are components of a mechanosensor in VSMCs.
最近的研究表明，某些上皮钠通道（ENaC）蛋白可能是血管平滑肌细胞中机械敏感离子通道复合物的组成部分，这些复合物会导致大脑中动脉（MCA）的压力诱导收缩。然而，特定的ENaC蛋白βENaC在MCA压力诱导收缩中的作用尚未确定。本研究的目的是确定在βENaC水平降低的小鼠模型中，MCA的压力诱导收缩是否会发生改变。通过定量免疫荧光，我们发现与野生型同窝小鼠（+/+）相比，βENaC纯合突变（m/m）小鼠脑血管平滑肌细胞（VSMC）中的全细胞βENaC标记被抑制了46%。分离出βENaC +/+和m/m小鼠的MCA，并将其置于血管腔室中进行肌电图分析。βENaC+/+小鼠的动脉随着灌注压力的逐步增加而收缩，在90 mmHg时产生的最大张力为10±2%（n = 5）。相比之下，βENaC m/m小鼠的MCA产生的张力明显较小（90 mmHg时为4±1%，n = 5）。两种基因型对氯化钾（4 - 80 mM）的血管收缩反应相同，对去氧肾上腺素（10(-7)-10(-4) M）的反应略有改变，这表明VSMC中βENaC水平的降低特异性地抑制了压力诱导的收缩。我们的研究结果表明，βENaC是MCA正常压力诱导收缩所必需的，并为βENaC蛋白是VSMC中机械传感器的组成部分这一假说提供了进一步的支持。
