成年大鼠心房肌牵张激活钾通道的牵张敏感性和门控机制

Mechanosensitivity and gating mechanism of stretch-activated potassium channels in adult rat atrial myocytes

目的探讨成年大鼠心房肌细胞牵张激活钾通道（stretch-activated K^＋-selective channels，SAKCs）的电生理学特性，确定皮质细胞骨架在通道门控机制中的作用，对从通道水平阐明机械-电反馈具有重要的理论和实际意义。方法联合应用单通道膜片钳技术和压力钳技术，在急性分离的成年大鼠心房肌细胞上，采用细胞贴附（cell-attached）方式记录SAKCs的活动。结果实验所记录的通道为SAKCs，通道闪烁样开放，无整流特性。当细胞外液为高K^＋液（140mmol／L）时，翻转电位为0mV。钳制膜电位＋60mV时单通道的电导值为（59±5）pS，-60mV时为（51±8）ps。通道约在负压刺激开始700～800ms内被快速激活，刺激解除后，通道快速在500ms内去激活。超过-30mmHg（1mmHg=0．133kPa）的刺激可使多个通道同时开放。实验中未观察到通道活动达到饱和现象。单通道电流幅度不受负压刺激的影响。随膜片钳电极内负压的增加，通道开放概率增大，呈刺激强度依赖性。Cytochalasin B不改变SAKCs的电流幅度，但增加SAKCs的开放概率，增强SAKCs的背景活动和对机械刺激的敏感性。结论我们推测生理状态下细胞皮质肌动蛋白内衬于细胞膜，可能作为细胞膜的并联成分承受部分细胞应力，并使脂质膜的应力减少，从而使SAKCs不易被激活。

AIM To discuss electrophysiological properties of SAKCs and to determine the effect of cortical skeleton in gating mechanism of SAKCs and to clarify MEF mechanism at channel level. METHODS Single-channel patch-clamp technique and pressure-clamp technique were simultaneously used to identify and characterize SAKCs of isolated adult rat atrial myocytes in cell-attached mode. RESULTS The stretch-activated channel current observed was K^＋ selective and not rectified with flickery bursts. The reversal potential was 0 mV when the atrial cell was in a high K^＋ （ 140 mmol/L） bath solution and the mean conductance was （59±5 ） pS and （51±8 ） pS at ＋ 60 mV and - 60 mV, respectively. The latency of channel＇s response to pressure steps Was 700 - 800 ms. After release of suction, the channels closed within 500 ms. Stretch beyond -30 mmHg resulted in multiple levels of channel opening. The SAKCs activity did not reach saturation before seal was destroyed. The single-channel conductance of SAKCs was insensitive to membrane stretch. The open probability of SAKCs increased in a pressure-dependent manner. Cytochalasin B did not change current amplitude of single SAKCs, but the open probability increased. Cytochalasin B increased mechanosensitivity of SAKCs and its background activity. CONCLUSION The cortical skeleton beneath the membrane in physiological condition might endure part of tension together with the membrane in parallel and might decrease the tension of the lipid bilayer. As a result, SAKCs are not easy to be activated.