title: Microdamage induced calcium efflux from bone matrix activates intracellular calcium signaling in osteoblasts via L-type and T-type voltage-gated calcium channels.
abstract: Mechanisms by which bone microdamage triggers repair response are not completely understood. It has been shown that calcium efflux ([Ca(2+)]E) occurs from regions of bone undergoing microdamage. Such efflux has also been shown to trigger intracellular calcium signaling ([Ca(2+)]I) in MC3T3-E1 cells local to damaged regions. Voltage-gated calcium channels (VGCCs) are implicated in the entry of [Ca(2+)]E to the cytoplasm. We investigated the involvement of VGCC in the extracellular calcium induced intracellular calcium response (ECIICR). MC3T3-E1 cells were subjected to one dimensional calcium efflux from their basal aspect which results in an increase in [Ca(2+)]I. This increase was concomitant with membrane depolarization and it was significantly reduced in the presence of Bepridil, a non-selective VGCC inhibitor. To identify specific type(s) of VGCC in ECIICR, the cells were treated with selective inhibitors for different types of VGCC. Significant changes in the peak intensity and the number of [Ca(2+)]I oscillations were observed when L-type and T-type specific VGCC inhibitors (Verapamil and NNC55-0396, respectively) were used. So as to confirm the involvement of L- and T-type VGCC in the context of microdamage, cells were seeded on devitalized notched bone specimen, which were loaded to induce microdamage in the presence and absence of Verapamil and NNC55-0396. The results showed significant decrease in [Ca(2+)]I activity of cells in the microdamaged regions of bone when L- and T-type blockers were applied. This study demonstrated that extracellular calcium increase in association with damage depolarizes the cell membrane and the calcium ions enter the cell cytoplasm by L- and T-type VGCCs.
authors.affiliation: Department of Mechanical and Aerospace Engineering, Case Western Reserve University, Cleveland, OH 44106, USA.
authors.forename: Hyungjin
authors.initials: H
authors.lastname: Jung
authors.affiliation: Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH 44106, USA.
authors.forename: Makenzie
authors.initials: M
authors.lastname: Best
authors.affiliation: Department of Mechanical and Aerospace Engineering, Case Western Reserve University, Cleveland, OH 44106, USA; Department of Orthopedics, Case Western Reserve University, Cleveland, OH 44106, USA; Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH 44106, USA. Electronic address: oxa@case.edu.
authors.forename: Ozan
authors.initials: O
authors.lastname: Akkus
mesh_terms: D016475:3T3 Cells; D000818:Animals; D001842:Bone and Bones / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000378:metabolism*; D020747:Calcium Channels, T-Type / Q000378:metabolism*; D020013:Calcium Signaling; D005453:Fluorescence; D015640:Ion Channel Gating; D017136:Ion Transport; D051379:Mice; D010006:Osteoblasts / Q000378:metabolism*
chemical_list: D020746:Calcium Channels, L-Type; D020747:Calcium Channels, T-Type; D002118:Calcium
keywords: Bone microdamage; Calcium channel inhibitor; Calcium efflux; Intracellular calcium signaling; Voltage-gated calcium channel