Abstract
Extracellular ATP released via pannexin-1 channels, in response to the activation of mechanosensitive-TRP channels during odontoblast mechanical stimulation, mediates intercellular communication among odontoblasts in dental pulp slice preparation dissected from rat incisor. Recently, odontoblast cell lines, such as mouse odontoblast lineage cells, have been widely used to investigate physiological/pathological cellular functions. To clarify whether the odontoblast cell lines also communicate with each other by diffusible chemical substance(s), we investigated the chemical intercellular communication among cells from mouse odontoblast cell lines following mechanical stimulation. A single cell was stimulated using a glass pipette filled with standard extracellular solution. We measured intracellular free Ca2+ concentration ([Ca2+]i) by fura-2 in stimulated cells, as well as in cells located nearby. Direct mechanical stimulation to a single odontoblast increased [Ca2+]i, which showed sensitivity to capsazepine. In addition, we observed increases in [Ca2+]i not only in the mechanically stimulated odontoblast, but also in nearby odontoblasts. We could observe mechanical stimulation-induced increase in [Ca2+]i in a stimulated human embryo kidney (HEK) 293 cell, but not in nearby HEK293 cells. The increase in [Ca2+]i in nearby odontoblasts, but not in the stimulated odontoblast, was inhibited by adenosine triphosphate (ATP) release channel (pannexin-1) inhibitor in a concentration- and spatial-dependent manner. Moreover, in the presence of phospholipase C (PLC) inhibitor, the increase in [Ca2+]i in nearby odontoblasts, following mechanical stimulation of a single odontoblast, was abolished. We could record some inward currents evoked from odontoblasts near the stimulated odontoblast, but the currents were observed in only 4.8% of the recorded odontoblasts. The results of this study showed that ATP is released via pannexin-1, from a mechanically stimulated odontoblast, which transmits a signal to nearby odontoblasts by predominant activation of PLC-coupled nucleotide receptors.
Highlights
Odontoblasts are dentin-forming cells that secrete dentin matrix proteins during physiological and pathological tooth formation
We demonstrated that intercellular signal transduction between mechanically stimulated and neighboring odontoblasts occurs via activation of mechanosensitive transient receptor potential (TRP) channels, release of adenosine triphosphate (ATP) from the pannexin-1 channel, and activation of phospholipase C (PLC)-coupled receptors
Since we previously reported that TRP Melastatin subfamily member 8 (TRPM8) channels are not expressed in mouse odontoblasts, CPZ-sensitive mechanical stimulation-induced [Ca2+]i response in the present study is mediated by TRPV1 channels
Summary
Odontoblasts are dentin-forming cells that secrete dentin matrix proteins during physiological and pathological tooth formation. The thermal, chemical, mechanical, and osmotic stimuli applied to the exposed dentin surface increase the hydrodynamic force and the velocity of dentinal fluid movement inside dentinal tubules (Andrew and Matthews, 2000; Charoenlarp et al, 2007). This increase in fluid movement induces deformation of plasma membrane of the odontoblast processes within the dentinal tubules (Magloire et al, 2010; Lin et al, 2011). Odontoblast cell membrane deformation activates various mechanosensitive-TRP channels as mechanosensors (Son et al, 2009; Tsumura et al, 2012; Shibukawa et al, 2015)
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