Activation of G protein-coupled parathyroid hormone receptors in rat incisor odontoblasts promotes mineralization via cyclic adenosine monophosphate, not Ca(2+) signalling: In vitro study.

AIM: Parathyroid hormone (PTH) and its Gα(s)-coupled receptors, PTH receptor, mediate odontoblast differentiation; however, the detailed intracellular adenylyl cyclase-mediated signalling pathway mediated by the PTH-PTH receptor axis remains to be elucidated. Therefore, we measured the intracellular levels of cyclic adenosine monophosphate (cAMP) in living single odontoblasts. METHODOLOGY: We obtained acutely isolated odontoblasts from newborn Wistar rats and analysed the mineralization ability by Alizarin red staining. Intracellular-free Ca(2+) concentration was measured using a fluorescent Ca(2+) indicator, whereas intracellular cAMP levels were examined by a mNeon Green-based cAMP sensor. RESULTS: Granulated PTH was detected in the vascular area of the dental pulp periphery. Application of the non-selective PTH receptor agonist DPC AJ1951 increased cAMP levels in odontoblasts. This increase was significantly inhibited by the non-selective PTH receptor antagonist 4185-v and the adenylyl cyclase inhibitor SQ 22536. However, applying the non-selective PTH receptor agonist DPC AJ1951 did not increase the intracellular Ca(2+) concentration without extracellular Ca(2+). In mineralization assays, PTH promoted mineralization by odontoblasts. The mineralization was inhibited by SQ 22536 and 4185-v but not by the phospholipase C inhibitor U73122. CONCLUSION: Thus, the present study suggests that PTH from the bloodstream functionally activates the Gα(s)-coupled PTH receptor in odontoblasts, which plays an essential role in dentinogenesis.