Intracellular Ca²⁺ Responses in Cultured Endothelial Cells to Mechanical Stimulation by Laser Tweezers

It is well known that endothelial cells (ECs) respond to the fluid imposed shear I stress and change their shapes and functions. We have focused on the importance of cytoplasmic micro-mechanical strain in mechano-sensing mechanism of ECs. To this end, the cytosolic Ca²⁺ responses of ECs to the mechanical stimulus by laser tweezers that can apply the micro-mechanical force to nano/micro-organisms without any physical contact, were investigated. When the laser spot focused on the nucleus of EC was slightly moved, the cytosolic Ca²⁺ increased immediately in the same EC, whereas there was no Ca²⁺ increase without laser spot movement. In the absence of extracellular Ca²⁺ in the medium or the blockade of stretch activated ion channels, there was also an increase of Ca²⁺ in stimulated ECs. Therefore, the increased Ca²⁺ in stimulated ECs is considered to be derived from intracellular Ca²⁺ store. The heterogeneous Ca²⁺ propagation from the stimulated EC to surrounding ECs was also observed. Two types of Ca²⁺ wave propagation were observed, the fast one that the velocity was more than 20μm/sec, and the slow one that the velocity was less than 1μm/sec. The micro-stress induced by the micro-movement of the nucleus can be a trigger of the cytosolic Ca²⁺ increase and the cytoplasmic micro-mechanical strain may play an important role in mechano-sensing mechanism of ECs.