Tran T A, Roger S, Le Guennec J Y, Tranquart F, Bouakaz A
INSERM U619, Tours, France.
Ultrasound Med Biol. 2007 Jan;33(1):158-63. doi: 10.1016/j.ultrasmedbio.2006.07.029.
New clinical applications of ultrasound contrast microbubbles extend beyond imaging and diagnosis toward therapeutic applications. Cell membrane permeability and the uptake of substances have been shown to be enhanced by microbubbles under ultrasound stimulation. However, the mechanisms of action of ultrasound-activated microbubbles are still unknown. The aim of our study was to examine how microbubbles and ultrasound interact with cells in an attempt to understand the sonoporation mechanism. The ruptured-patch-clamp whole-cell technique was used to measure membrane potential variations of a single cell. SonoVue microbubbles and mammary breast cancer cell line MDA-MB-231 were used. Ultrasound was applied using single-element transducers of 1 MHz. Microbubbles and cells were simultaneously video monitored during ultrasound exposure. Our results showed that, during sonoporation, a marked cell membrane hyperpolarization occurs (n = 6 cells) at negative pressures above 150 kPa, indicating the activation of specific ion channels while the cell and the microbubbles remain viable. The hyperpolarization was sustained for as long as the microbubbles are in a direct contact with the cell and the ultrasound waves are transmitted. Smaller acoustic amplitudes induced only mild hyperpolarization, whereas shutting off the ultrasound brings the cell membrane potential to its resting value. However, ultrasound alone did not affect the cell membrane potential. A similar hyperpolarization of the cell membrane was observed when a mechanical pressure was applied on the cell through a glass probe. In conclusion, the results demonstrate that microbubbles' oscillations under ultrasound activation entail modifications of the electrophysiologic cell activities by triggering the modulation of ionic transports through the plasmic cell membrane. However, only cells in direct contact with the microbubbles are impacted. The mechanisms involved are likely related to activation of specific channels sensitive to mechanical stresses (stretch-activated channels) and possibly nonspecific ion channels.
超声造影微泡的新临床应用已从成像和诊断扩展到治疗应用。研究表明，在超声刺激下，微泡可增强细胞膜通透性和物质摄取。然而，超声激活微泡的作用机制仍不清楚。我们研究的目的是研究微泡和超声如何与细胞相互作用，以试图了解声孔效应机制。采用破膜片钳全细胞技术测量单个细胞的膜电位变化。使用了声诺维微泡和乳腺癌细胞系MDA-MB-231。使用1MHz的单元素换能器施加超声。在超声照射期间，对微泡和细胞进行同步视频监测。我们的结果表明，在声孔效应过程中，当负压高于150kPa时，会出现明显的细胞膜超极化（n = 6个细胞），这表明在细胞和微泡保持存活的同时，特定离子通道被激活。只要微泡与细胞直接接触且超声波被传输，超极化就会持续。较小的声振幅仅引起轻微的超极化，而关闭超声会使细胞膜电位恢复到静息值。然而，单独的超声不会影响细胞膜电位。当通过玻璃探针向细胞施加机械压力时，观察到细胞膜有类似的超极化。总之，结果表明，超声激活下微泡的振荡通过触发对穿过细胞质膜的离子转运的调节，引起细胞电生理活动的改变。然而，只有与微泡直接接触的细胞会受到影响。所涉及的机制可能与对机械应力敏感的特定通道（牵张激活通道）以及可能的非特异性离子通道的激活有关。
