Plasma Membrane Mechanical Stress Activates TRPC5 Channels

Mechanical forces exerted on cells impose stress on the plasma membrane. Cells sense this stress and elicit a mechanoelectric transduction cascade that initiates compensatory mechanisms. Mechanosensitive ion channels in the plasma membrane are responsible for transducing the mechanical signals to electrical signals. However, the mechanisms underlying channel activation in response to mechanical stress remain incompletely understood. Transient Receptor Potential (TRP) channels serve essential functions in several sensory modalities. These channels can also participate in mechanotransduction by either being autonomously sensitive to mechanical perturbation or by coupling to other mechanosensory components of the cell. Here, we investigated the response of a TRP family member, TRPC5, to mechanical stress. Hypoosmolarity triggers Ca2+ influx and cationic conductance through TRPC5. Importantly, for the first time we were able to record the stretch-activated TRPC5 current at single-channel level. The activation threshold for TRPC5 was found to be 240 mOsm for hypoosmotic stress and between −20 and −40 mmHg for pressure applied to membrane patch. In addition, we found that disruption of actin filaments suppresses TRPC5 response to hypoosmotic stress and patch pipette pressure, but does not prevent the activation of TRPC5 by stretch-independent mechanisms, indicating that actin cytoskeleton is an essential transduction component that confers mechanosensitivity to TRPC5. In summary, our findings establish that TRPC5 can be activated at the single-channel level when mechanical stress on the cell reaches a certain threshold.施加于细胞的机械力会对质膜（plasma membrane）产生应力。细胞可感知此类应力，并触发机电转导级联反应，进而启动代偿机制。质膜中的机械敏感性离子通道（mechanosensitive ion channels）负责将机械信号转换为电信号。然而，当前人们对机械应力激活离子通道的具体分子机制仍未完全阐明。瞬时受体电位（Transient Receptor Potential, TRP）通道在多种感觉模态中发挥关键功能，此类通道既可通过自身对机械扰动的敏感性，亦可通过与细胞其他机械感觉组分偶联的方式参与机械转导过程。本研究针对TRP家族成员TRPC5对机械应力的响应展开了探究。低渗刺激可通过TRPC5引发钙离子（Ca²+）内流及阳离子电导。尤为重要的是，本研究首次在单通道水平记录到了牵张激活的TRPC5电流。研究发现，TRPC5的激活阈值为：低渗应激条件下为240 mOsm，膜片施加负压时为-20至-40 mmHg。此外，本研究还发现，肌动蛋白丝（actin filaments）的解聚会抑制TRPC5对低渗应激及膜片施加负压的响应，但无法阻断非牵张依赖性机制对TRPC5的激活，这表明肌动蛋白细胞骨架（actin cytoskeleton）是赋予TRPC5机械敏感性的关键转导组分。综上，本研究结果证实，当细胞所受机械应力达到特定阈值时，TRPC5可在单通道水平被激活。