Calcium influx through stretch-activated channels mediates microfilament reorganization in osteoblasts under simulated weightlessness

We have explored the role of Ca ²⁺ signaling in microfilament reorganization of osteoblasts induced by simulated weightlessness using a random positioning machine (RPM). The RPM-induced alterations of cell morphology, microfilament distribution, cell proliferation, cell migration, cytosol free calcium concentration ([Ca ²⁺ ] _i ), and protein expression in MG63 osteoblasts were investigated. Simulated weightlessness reduced cell size, disrupted microfilament, inhibited cellular proliferation and migration, and induced an increase in [Ca ²⁺ ] _i in MG63 human osteosarcoma cells. Gadolinium chloride (Gd), an inhibitor for stretch-activated channels, attenuated the increase in [Ca ²⁺ ] _i and microfilament disruption. Further, the expression of calmodulin was significantly increased by simulated weightlessness, and an inhibitor of calmodulin, W-7, aggravated microfilament disruption. Our findings demonstrate that simulated weightlessness induces Ca ²⁺ influx through stretch-activated channels, then results in microfilament disruption.