Akinlaja J, Sachs F
Department of Physics, State University of New York, Buffalo, New York 14214, USA.
Biophys J. 1998 Jul;75(1):247-54. doi: 10.1016/S0006-3495(98)77511-3.
We attempted to determine whether mechanical tension and electrical stress couple to cause membrane breakdown in cells. Using cell-attached patches from HEK293 cells, we estimated the mechanically produced tension from the applied pressure and geometry of the patch. Voltage pulses of increasing amplitude were applied until we observed a sudden increase in conductance and capacitance. For pulses of 50 micros duration, breakdown required >0.5 V and was dependent on the tension. For pulses of 50-100 ms duration, breakdown required 0.2-0.4 V and was independent of tension. Apparently two physically different processes can lead to membrane breakdown. We could explain the response to the short, high-voltage pulses if breakdown occurred in the lipid bilayer. The critical electromechanical energy per unit area for breakdown by short pulses was approximately 4 dyne/cm, in agreement with earlier results on bilayers. Our data suggest that, at least in a patch, the bilayer may hold a significant fraction (approximately 40%) of the mean tension. To be compatible with the large, nonlytic area changes of patches, the bilayer appears to be pulled toward the pipette tip, perhaps by hydrophobic forces wetting membrane proteins bound to the glass. Although breakdown voltages for long pulses were in agreement with earlier work on algae, the mechanism(s) for this breakdown remain unclear.
我们试图确定机械张力和电应力是否相互耦合导致细胞中的膜破裂。使用来自HEK293细胞的细胞贴附膜片，我们根据施加的压力和膜片的几何形状估算机械产生的张力。施加幅度逐渐增加的电压脉冲，直到我们观察到电导和电容突然增加。对于持续时间为50微秒的脉冲，破裂需要>0.5伏，并且取决于张力。对于持续时间为50 - 100毫秒的脉冲，破裂需要0.2 - 0.4伏，并且与张力无关。显然，两个物理上不同的过程可导致膜破裂。如果在脂质双层中发生破裂，我们可以解释对短的高压脉冲的响应。短脉冲导致破裂的每单位面积的临界机电能量约为4达因/厘米，与早期关于双层的结果一致。我们的数据表明，至少在一个膜片中，双层可能承受平均张力的很大一部分（约40%）。为了与膜片的大的非裂解面积变化相兼容，双层似乎被拉向移液器尖端，可能是通过润湿与玻璃结合的膜蛋白的疏水作用力。尽管长脉冲的破裂电压与早期关于藻类的研究结果一致，但这种破裂的机制仍不清楚。
