Effects of mechanical pressure on intracellular calcium release channel and cytoskeletal structure in rabbit mandibular condylar chondrocytes

Many signal molecules are involved in mechanotransduction process, among which intracellular calcium and cytoskeleton are two of the most important ones. This study investigated the changes of intracellular calcium and cytoskeleton under pressure and the effects of intracellular calcium variation on cytoskeleton responses to the pressure in rabbit mandibular condylar chondrocytes (MCCs). In vitro cultured MCCs from 2-week-old New Zealand rabbits were incubated for observation of intracellular calcium variation under laser scanning microscope. Coomassie BB staining was used to observe the characteristics of cytoskeleton. We found that intracellular calcium increased following the irritation by 1,25(OH)2D3, whereas it remained unchanged when inositol triphosphate receptor (IP3R) channel was blocked by heparin. Pretreatment with pressure of 90 kPa for 60 min enhanced the sensitivity of IP3R channel and caused higher intracellular calcium concentration. The cytoskeletons of MCCs were revealed correspondingly uniform and reticular in the control, most of which showed higher expression in tighter arrangement under continuous pressure of 90 kPa for 60 min but lower expression when the pressure time was prolonged to 360 min. When MCCs were pretreated with heparin, the cytoskeleton of them displayed sparsely and discontinuously under 90 kPa for 60 min. To sum up, both cytoskeleton and intracellular calcium participate in the transition process of mechanical signal to biological effects of MCC. However, the decrease of intracellular calcium resulted from IP3R channel blocking obviously interferes the recomposition of cytoskeleton under mechanical pressure, which suggests that calcium message is indispensable to the cytoskeleton response of MCC under pressure.