Abstract：
Chondrocytes respond to mechanical stimuli by increasing their intracellular calcium concentration. The response depends on the cellular environment. Previous studies have investigated chondrocytes under slow strain rates or cells embedded in hydrogels, but the response of chondrocytes in their native environment under physiologically relevant cyclic loads and dynamic hydrostatic pressure has not been studied. This study investigated the calcium signaling response of in-situ chondrocytes under physiological cyclic compressive loads and hydrostatic pressure with varying frequency and load rates. Bovine cartilage explants were stained with a fluorescent calcium indicator dye and subjected to physiologically relevant cyclic loads using a custom-built loading device secured on a confocal/multiphoton microscope. Calcium fluorescence intensities of the cells were tracked and analyzed. Loading groups were compared using one-way ANOVA followed by a post-hoc test with Tukey correction (α = 0.05). The percentage of cells signaling increased in all compressive loading conditions compared to the no-load baseline. The percentage of cells responding under 1 Hz load was significantly greater than the slow ramp and 0.1 Hz group (p < 0.05). The number of compression cycles had no effect on the calcium signaling response (p > 0.05). The width and time between consecutive peaks were not different between different loading conditions (p > 0.05). Calcium signaling of in-situ chondrocytes did not increase under dynamic hydrostatic pressure of magnitudes up to 0.2 MPa at frequencies of 0.5 Hz and 0.05 Hz (p > 0.05). In conclusion, in-situ chondrocytes respond to physiological compressive loads in a strain rate-dependent manner with an increased number of responsive cells and unaltered temporal characteristics.
摘要：
软骨细胞通过增加细胞内钙浓度来响应机械刺激。响应取决于蜂窝环境。以前的研究已经研究了缓慢应变速率下的软骨细胞或嵌入水凝胶中的细胞，但是尚未研究软骨细胞在其天然环境中在生理相关的循环负荷和动态静水压力下的反应。这项研究调查了原位软骨细胞在生理循环压缩载荷和静水压力下以不同频率和载荷速率的钙信号响应。用荧光钙指示剂染料对牛软骨外植体进行染色，并使用固定在共聚焦/多光子显微镜上的定制加载装置进行生理相关的循环加载。追踪并分析细胞的钙荧光强度。使用单向ANOVA比较负载组，然后进行Tukey校正后的事后检验（α=0.05）。与无负载基线相比,细胞信号传导的百分比在所有压缩负载条件下增加。在1Hz负荷下响应的细胞百分比显著大于慢斜坡和0.1Hz组(p<0.05)。压缩循环次数对钙信号应答没有影响(p>0.05)。连续峰之间的宽度和时间在不同负载条件下没有差异(p>0.05)。在0.5Hz和0.05Hz的频率下，在高达0.2MPa的动态静水压力下，原位软骨细胞的钙信号传导没有增加（p>0.05）。总之,原位软骨细胞以应变率依赖性方式响应生理压缩载荷，响应细胞数量增加，时间特征不变。
