High pH-Sensitive TRPA1 Activation in Odontoblasts Regulates Mineralization

Calcium hydroxide and mineral trioxide aggregate are widely used for indirect and direct pulp capping and root canal filling. their dissociation into ca2+ and oh- in dental pulp creates an alkaline environment,which activates reparative/reactionary dentinogenesis. however,the mechanisms by which odontoblasts detect the ph of the extracellular environment remain unclear. we examined the alkali-sensitive intracellular ca2+ signaling pathway in rat odontoblasts. in the presence or absence of extracellular ca2+,application of alkaline solution increased intracellular ca2+ concentration,or [ca2+]i. alkaline solution-induced [ca2+]i increases depended on extracellular ph (8.5 to 10.5) in both the absence and the presence of extracellular ca2+. the amplitude was smaller in the absence than in the presence of extracellular ca2+. each increase in [ca2+]i,activated by ph 7.5,8.5,or 9.5,depended on extracellular ca2+ concentration; the equilibrium binding constant for extracellular ca2+ concentration decreased as extracellular ph increased (1.04 mm at ph 7.5 to 0.11 mm at ph 9.5). repeated applications of alkaline solution did not have a desensitizing effect on alkali-induced [ca2+]i increases and inward currents. in the presence of extracellular ca2+,alkaline solution-induced [ca2+]i increases were suppressed by application of an antagonist of transient receptor potential ankyrin subfamily member 1 (trpa1) channels. ca2+ exclusion efficiency during alkaline solution-induced [ca2+]i increases was reduced by a na+-ca2+ exchanger antagonist. alizarin red and von kossa staining revealed increased mineralization levels under repeated high ph stimulation,whereas the trpa1 antagonist strongly reduced this effect. these findings indicate that alkaline stimuli - such as the alkaline environment inside dental pulp treated with calcium hydroxide or mineral trioxide aggregate - activate ca2+ mobilization via ca2+ influx mediated by trpa1 channels and intracellular ca2+ release in odontoblasts. high ph-sensing mechanisms in odontoblasts are important for activating dentinogenesis induced by an alkaline environment. © international & american associations for dental research.