Calcium Signaling in Bone Cell Networks Induced by Fluid Flow

Mechanical stimuli such as fluid flow can induce robust multiple intracellular calcium ([Ca²⁺]_i) peaks in connected bone cell networks [1]. This fluid flow induced oscillation of [Ca²⁺]_i can come from two sources: intracellular Ca²⁺ stores (e.g., endoplasmic reticulum, ER) and the extracellular environment. Moreover, [Ca²⁺]_i signaling is mediated by various molecular pathways, such as IP₃, ATP, PGE₂, and NO. Osteocytes are believed to comprise a sensory network in bone tissue that monitors in vivo mechanical loading and triggers appropriate adaptive responses from osteoblasts and osteoclasts [2]. It is also well recognized that osteoblasts, the cells responsible for bone formation, can directly sense and respond to mechanical stimulation (e.g., fluid flow). In the present study, two types of cell networks were constructed in vitro with osteocyte-like and osteoblast-like cells, respectively, by using microcontact printing and self assembled monolayer (SAM) technologies. The calcium responses of the two types of cell networks to fluid flow were recorded, quantitatively analyzed, and compared. Then we examined how the [Ca²⁺]_i response in the osteocyte cell network was influenced by gap junctions, intra/extracellular calcium sources, and other various molecular pathways.