Inserted rest period resensitizes MC3T3-E1 cells to fluid shear stress in a time-dependent manner via F-actin-regulated mechanosensitive channel(s).

The underlying cellular mechanism of anabolic effect recovered by inserting rest is not fully understood. In this work, we studied the role of F-actin regulated mechanosensitive channel(s) re-activation in mechanosensitivity modulation in vitro. Results showed that steady fluid shear stress (sFSS) stimulation with 30-min rest period was more potential in increasing alkalinephosphatase (ALP) activity than 10 and 0-min rest periods, and insertion of 30 min, but not 0 or 10 min, recovered the [Ca(2+)]i transient and contribution of the mechanosensitive channel(s). During the rest period, F-actin experienced polymerization (0-10 min), followed by depolymerization (10-30 min); inhibition of F-actin polymerization/depolymerization significantly increased/decreased the [Ca(2+)]i transient, as well as the contribution of the mechanosensitive channel(s) in subsequent sFSS stimulation. Our results demonstrated that the long rest period between sFSS loadings recruited [Ca(2+)]i transient via F-actin depolymerization-induced reactivation of mechanosensitive channel(s), suggesting that F-actin-regulated cellular stiffness could account for the decreased anabolic response during continuous mechanical loading in bone cells.