Mechanosensitive channel properties and membrane mechanics in mouse dystrophic myotubes
Mechanosensitive channel properties and membrane mechanics in mouse dystrophic myotubes
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DOI：
10.1113/jphysiol.2006.125021
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发表时间：
2007-05-15
影响因子：
5.5
通讯作者：
Sachs, Frederick
中科院分区：
文献类型：
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作者：
Suchyna, Thomas M.;Sachs, Frederick
肌营养不良症与机械敏感通道 (MSC) 活性增加和细胞钙水平增加有关。与野生型小鼠的斑块相比，mdx 小鼠肌管斑块中的 MSC 具有更高水平的静息活性，并且激活和失活的潜伏期明显。贴片电容和几何形状的测量表明，这些差异与皮质膜力学有关，而不是与通道门控的差异有关。我们意外地发现，mdx 小鼠的斑块由于肌动蛋白垂直于膜的拉力而强烈地向移液器尖端弯曲。这种力产生很大的张力（类似于 5 mN m(-1)），可以在没有明显刺激的情况下激活 MSC。肌动蛋白抑制剂消除了 mdx 小鼠斑块的向内弯曲。对移液器施加适度的吸力会使膜变平，减少张力，并使反应看起来像是拉伸失活的。 mdx 小鼠斑块中明显的激活潜伏期是由将皮层从向内弯曲到向外弯曲重组所需的机械松弛时间引起的。增加的潜伏期相当于皮质粘度增加了三倍。通过化学或机械手段破坏细胞骨架，消除了野生型和 mdx 小鼠斑块之间动力学和曲率的差异。拉伸引起的贴片比电容增加（类似于 80 fF mu m(-2)），远远超过双层的比电容，表明存在对大膜池（可能是小窝、T 管或千兆密封部分）的应力敏感通道。在 mdx 小鼠细胞中，快速电压敏感失活的固有门控特性丢失。它在野生型小鼠细胞中很强大（在 50% 的outside-out patch 中观察到），但从未在 mdx 细胞中观察到。肌营养不良蛋白和失活之间的这种联系可能导致背景阳离子电流和 Ca 21 流入增加。 mdx 小鼠细胞中的自发 Ca2+ 瞬变对去极化敏感，并受到 D 型和 L 型特定 MSC 抑制剂 GsMTx4 的抑制。
Muscular dystrophy is associated with increased activity of mechanosensitive channels (MSCs) and increased cell calcium levels. MSCs in patches from mdx mouse myotubes have higher levels of resting activity, compared to patches from wild-type mice, and a pronounced latency of activation and deactivation. Measurements of patch capacitance and geometry reveal that the differences are linked to cortical membrane mechanics rather than to differences in channel gating. We found unexpectedly that patches from mdx mice are strongly curved towards the pipette tip by actin pulling normal to the membrane. This force produces a substantial tension (similar to 5 mN m(-1)) that can activate MSCs in the absence of overt stimulation. The inward curvature of patches from mdx mice is eliminated by actin inhibitors. Applying moderate suction to the pipette flattens the membrane, reducing tension, and making the response appear to be stretch inactivated. The pronounced latency to activation in patches from mdx mice is caused by the mechanical relaxation time required to reorganize the cortex from inward to outward curvature. The increased latency is equivalent to a three-fold increase in cortical viscosity. Disruption of the cytoskeleton by chemical or mechanical means eliminates the differences in kinetics and curvature between patches from wild-type and mdx mice. The stretch-induced increase in specific capacitance of the patch, similar to 80 fF mu m(-2), far exceeds the specific capacitance of bilayers, suggesting the presence of stress-sensitive access to large pools of membrane, possibly caveoli, T-tubules or portions of the gigaseal. In mdx mouse cells the intrinsic gating property of fast voltage-sensitive inactivation is lost. It is robust in wild-type mouse cells (observed in 50% of outside-out patches), but never observed in mdx cells. This link between dystrophin and inactivation may lead to increased background cation currents and Ca 21 influx. Spontaneous Ca2+ transients in mdx mouse cells are sensitive to depolarization and are inhibited by the specific MSC inhibitor GsMTx4, in both the D and L forms.