Elevation of extracellular ca2+ induces store-operated calcium entry via calcium-sensing receptors: A pathway contributes to the proliferation of osteoblasts

Abstract

Methods: Cytosolic Ca2+concentration ([Ca2+]c) of primary cultured rat osteoblasts was detected by fluorescence imaging using calcium-sensitive probe fura-2/AM. Osteoblastic proliferation was estimated by cell counting, MTS assay and ATP assay. Agonists and antagonists of calcium-sensing receptors (CaSR) as well as inhibitors of phospholipase C (PLC), SOCE and voltage-gated calcium (Cav) channels were applied to study the mechanism in detail. Aims: The local concentration of extracellular Ca2+([Ca2+]o) in bone microenvironment is accumulated during bone remodeling. In the present study we investigated whether elevating [Ca2+]oinduced store-operated calcium entry (SOCE) in primary rat calvarial osteoblasts and further examined the contribution of elevating [Ca2+]oto osteoblastic proliferation. Results: Our data showed that elevating [Ca2+]oevoked a sustained increase of [Ca2+]cin a dose-dependent manner. This [Ca2+]cincrease was blocked by TMB-8 (Ca2+release inhibitor), 2-APB and BTP-2 (both SOCE blockers), respectively, whereas not affected by Cav channels blockers nifedipine and verapamil. Furthermore, NPS2143 (a CaSR antagonist) or U73122 (a PLC inhibitor) strongly reduced the [Ca2+]o-induced [Ca2+]cincrease. The similar responses were observed when cells were stimulated with CaSR agonist spermine. These data indicated that elevating [Ca2+]oresulted in SOCE depending on the activation of CaSR and PLC in osteoblasts. In addition, high [Ca2+]osignificantly promoted osteoblastic proliferation, which was notably reversed by BAPTA-AM (an intracellular calcium chelator), 2-APB, BTP-2, TMB-8, NPS2143 and U73122, respectively, but not affected by Cav channels antagonists. Conclusions: Elevating [Ca2+]oinduced SOCE by triggering the activation of CaSR and PLC. This process was involved in osteoblastic proliferation induced by high level of extracellular Ca2+concentration.