Department of Physiology and Biophysics, University of Mississippi Medical Center, Jackson, MS 39216, USA.
Am J Physiol Renal Physiol. 2013 Jun 15;304(12):F1428-37. doi: 10.1152/ajprenal.00444.2012. Epub 2013 Apr 3.
Myogenic constrictor responses in small renal arteries and afferent arterioles are suppressed in mice with reduced levels of β-epithelial Na⁺ channel (βENaC(m/m)). The underlying mechanism is unclear. Decreased activity of voltage-gated calcium channels (VGCC) or mechanically gated ion channels and increased activity of large conductance calcium-activated potassium (BK) channels are a few possible mechanisms. The purpose of this study was to determine if VGCC, BK, or mechanically gated ion channel activity was altered in renal vascular smooth muscle cell (VSMC) from βENaC(m/m) mice. To address this, we used whole cell patch-clamp electrophysiological approaches in freshly isolated renal VSMCs. Compared with βENaC(+/+) controls, the current-voltage relationships for VGCC and BK activity are similar in βENaC(m/m) mice. These findings suggest neither VGCC nor BK channel dysfunction accounts for reduced myogenic constriction in βENaC(m/m) mice. We then examined mechanically gated currents using a novel in vitro assay where VSMCs are mechanically activated by stretching an underlying elastomer. We found the mechanically gated currents, predominantly carried by Na⁺, are observed with less frequency (87 vs. 43%) and have smaller magnitude (-54.1 ± 12.5 vs. -20.9 ± 4.9 pA) in renal VSMCs from βENaC(m/m) mice. Residual currents are expected in this model since VSMC βENaC expression is reduced by 50%. These findings suggest βENaC is required for normal mechanically gated currents in renal VSMCs and their disruption may account for the reduced myogenic constriction in the βENaC(m/m) model. Our findings are consistent with the role of βENaC as a VSMC mechanosensor and function of evolutionarily related nematode degenerin proteins.
在β-上皮钠通道（βENaC(m/m)）水平降低的小鼠中，小肾动脉和入球小动脉的肌源性收缩反应受到抑制。其潜在机制尚不清楚。电压门控钙通道（VGCC）或机械门控离子通道活性降低以及大电导钙激活钾（BK）通道活性增加是几种可能的机制。本研究的目的是确定βENaC(m/m)小鼠肾血管平滑肌细胞（VSMC）中 VGCC、BK 或机械门控离子通道活性是否发生改变。为了解决这个问题，我们使用了新鲜分离的肾 VSMC 的全细胞膜片钳电生理学方法。与βENaC(+/+)对照相比，βENaC(m/m)小鼠中 VGCC 和 BK 活性的电流-电压关系相似。这些发现表明，βENaC(m/m)小鼠肌源性收缩减少既不是 VGCC 也不是 BK 通道功能障碍所致。然后，我们使用一种新的体外测定方法来检查机械门控电流，其中通过拉伸下面的弹性体使 VSMC 机械激活。我们发现，机械门控电流（主要由 Na⁺携带）的出现频率较低（87%比 43%），幅度较小（-54.1 ± 12.5 比 -20.9 ± 4.9 pA）在βENaC(m/m)小鼠的肾 VSMC 中。由于 VSMC 的βENaC 表达减少了 50%，因此预计在这种模型中会有残留电流。这些发现表明βENaC 是正常机械门控电流在肾 VSMC 中所必需的，其破坏可能导致βENaC(m/m)模型中肌源性收缩减少。我们的发现与βENaC 作为 VSMC 机械感受器的作用以及进化上相关的线虫退行性蛋白的功能一致。
