title: Fluid shear stress induces calcium transients in osteoblasts through depolarization of osteoblastic membrane.
abstract: Intracellular calcium transient ([Ca(2+)]i transient) induced by fluid shear stress (FSS) plays an important role in osteoblastic mechanotransduction. Changes of membrane potential usually affect [Ca(2+)]i level. Here, we sought to determine whether there was a relationship between membrane potential and FSS-induced [Ca(2+)]i transient in osteoblasts. Fluorescent dyes DiBAC4(3) and fura-2AM were respectively used to detect membrane potential and [Ca(2+)]i. Our results showed that FSS firstly induced depolarization of membrane potential and then a transient rising of [Ca(2+)]i in osteoblasts. There was a same threshold for FSS to induce depolarization of membrane potential and [Ca(2+)]i transients. Replacing extracellular Na(+) with tetraethylammonium or blocking stretch-activated channels (SACs) with gadolinium both effectively inhibited FSS-induced membrane depolarization and [Ca(2+)]i transients. However, voltage-activated K(+) channel inhibitor, 4-Aminopyridine, did not affect these responses. Removing extracellular Ca(2+) or blocking of L-type voltage-sensitive Ca(2+) channels (L-VSCCs) with nifedipine inhibited FSS-induced [Ca(2+)]i transients in osteoblasts too. Quantifying membrane potential with patch clamp showed that the resting potential of osteoblasts was -43.3mV and the depolarization induced by FSS was about 44mV. Voltage clamp indicated that this depolarization was enough to activated L-VSCCs in osteoblasts. These results suggested a time line of Ca(2+) mobilization wherein FSS activated SACs to promote Na(+) entry to depolarize membrane that, in turn, activated L-VSCCs and Ca(2+) influx though L-VSCCs switched on [Ca(2+)]i response in osteoblasts.
authors.affiliation: The Key Laboratory of Biomedical Information Engineering of Ministry of Education, School of Life Science and Technology, Xi׳an Jiaotong University, Xi׳an 710049, China.
authors.forename: Junqing
authors.initials: J
authors.lastname: Sun
authors.affiliation: The Key Laboratory of Biomedical Information Engineering of Ministry of Education, School of Life Science and Technology, Xi׳an Jiaotong University, Xi׳an 710049, China; Hong-hui Hospital, College of Medicine, Xi׳an Jiaotong University, Xi׳an 710054, China.
authors.forename: Xifang
authors.initials: X
authors.lastname: Liu
authors.affiliation: The Key Laboratory of Biomedical Information Engineering of Ministry of Education, School of Life Science and Technology, Xi׳an Jiaotong University, Xi׳an 710049, China.
authors.forename: Jie
authors.initials: J
authors.lastname: Tong
authors.affiliation: The Key Laboratory of Biomedical Information Engineering of Ministry of Education, School of Life Science and Technology, Xi׳an Jiaotong University, Xi׳an 710049, China.
authors.forename: Lijun
authors.initials: L
authors.lastname: Sun
authors.affiliation: The Key Laboratory of Biomedical Information Engineering of Ministry of Education, School of Life Science and Technology, Xi׳an Jiaotong University, Xi׳an 710049, China.
authors.forename: Hao
authors.initials: H
authors.lastname: Xu
authors.affiliation: The Key Laboratory of Biomedical Information Engineering of Ministry of Education, School of Life Science and Technology, Xi׳an Jiaotong University, Xi׳an 710049, China.
authors.forename: Liang
authors.initials: L
authors.lastname: Shi
authors.affiliation: The Key Laboratory of Biomedical Information Engineering of Ministry of Education, School of Life Science and Technology, Xi׳an Jiaotong University, Xi׳an 710049, China. Electronic address: zhangjb@mail.xjtu.edu.cn.
authors.forename: Jianbao
authors.initials: J
authors.lastname: Zhang
mesh_terms: D016475:3T3 Cells; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000378:metabolism*; D016257:Fura-2 / Q000031:analogs & derivatives; D040542:Mechanotransduction, Cellular; D008564:Membrane Potentials; D051379:Mice; D009543:Nifedipine; D010006:Osteoblasts / Q000378:metabolism*; D013314:Stress, Mechanical
chemical_list: D020746:Calcium Channels, L-Type; C049925:fura-2-am; D009543:Nifedipine; D002118:Calcium; D016257:Fura-2
keywords: Ca(2+) transient; Fluid shear stress; Membrane potential; Osteoblast