Abstract
Odontoblasts play a crucial role in dentin formation and sensory transduction following the application of stimuli to the dentin surface. Various exogenous and endogenous stimuli elicit an increase in the intracellular free calcium concentration ([Ca2+]i) in odontoblasts, which is mediated by Ca2+ release from intracellular Ca2+ stores and/or Ca2+ influx from the extracellular medium. In a previous study, we demonstrated that the depletion of Ca2+ stores in odontoblasts activated store-operated Ca2+ entry (SOCE), a Ca2+ influx pathway. However, the precise biophysical and pharmacological properties of SOCE in odontoblasts have remained unclear. In the present study, we examined the functional expression and pharmacological properties of Ca2+ release-activated Ca2+ (CRAC) channels that mediate SOCE and evaluated the alkali sensitivity of SOCE in rat odontoblasts. In the absence of extracellular Ca2+, treatment with thapsigargin (TG), a sarco/endoplasmic reticulum Ca2+-ATPase inhibitor, induced an increase in [Ca2+]i. After [Ca2+]i returned to near-resting levels, the subsequent application of 2.5 mM extracellular Ca2+ resulted in an increase in [Ca2+]i which is a typical of SOCE activation. Additionally, application of 2-methylthioadenosine diphosphate trisodium salt (2-MeSADP), a P2Y1,12,13 receptor agonist, or carbachol (CCh), a muscarinic cholinergic receptor agonist, in the absence of extracellular Ca2+, induced a transient increase in [Ca2+]i. The subsequent addition of extracellular Ca2+ resulted in significantly higher [Ca2+]i in 2-MeSADP- or CCh-treated odontoblasts than in untreated cells. SOCE, that is activated by addition of extracellular Ca2+ in the TG pretreated odontoblasts was then suppressed by Synta66, BTP2, or lanthanum, which are CRAC channel inhibitors. Treatment with an alkaline solution enhanced SOCE, while treatment with HC030031, a TRPA1 channel antagonist, inhibited it. The amplitude of SOCE at pH 9 in the presence of HC030031 was higher than that at pH 7.4 in the absence of HC030031. These findings indicate that CRAC channel-mediated alkali-sensitive SOCE occurs in odontoblasts. SOCE is mediated by P2Y and muscarinic-cholinergic receptors, which are activated by endogenous ligands in odontoblasts.
Highlights
Alkaline solution containing Ca2+ enhanced store-operated Ca2+ entry (SOCE) under TRPA1 channel inhibition, compared to that using the extracellular solution with Ca2+ without TRPA1 inhibition
These results indicate that, in odontoblasts, store depletion activates Ca2+ release-activated Ca2+ (CRAC) channel-mediated SOCE, which is promoted in an alkaline environment
The results are in line with previous results showing the expression of Orai1, subunits of CRAC channels, by immunohistochemical analysis in odontoblasts (Zheng et al, 2015)
Summary
Along with their role in physiological dentin formation and mineralization (dentinogenesis), odontoblasts are important players in sensory transduction following various stimuli to the dentin surface (Linde, 1995; Linde and Lundgren, 1995; Tsumura et al, 2012, 2013; Sato et al, 2013, 2015; Shibukawa et al, 2015; Kimura et al, 2016; Nishiyama et al, 2016). IP3 activates the Ca2+ permeable IP3 receptor channels on the Ca2+ stores (Rhee and Bae, 1997; Syrovatkina et al, 2016) Both Ca2+ influx from extracellular medium and Ca2+ release from Ca2+ stores increase [Ca2+]i, and the increased intracellular Ca2+ is extruded to the extracellular medium via Na+-Ca2+ exchanger (NCX) subtypes 1, and 3 (Lundgren and Linde, 1988; Lundquist et al, 2000; Tsumura et al, 2010), and/or Ca2+–ATPase (PMCA) (Linde and Lundgren, 1995) in the distal end of plasma membrane in odontoblasts. The increased intracellular Ca2+ is taken up into the Ca2+ stores via sarco-endoplasmic reticulum Ca2+–ATPase (SERCA) (refilling) (Lundgren and Linde, 1997)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
