Ca(2+) signaling mediated by IP(3)-dependent Ca(2+) releasing and store-operated Ca(2+) channels in rat odontoblasts

In the phospholipase-C (PLC) signaling system, Ca(2+) is mobilized from intracellular Ca(2+) stores by an action of inositol 1,4,5-trisphosphate (IP(3)). The depletion Of IP(3)-sensitive Ca(2+) stores activates a store-operated Ca2+ entry (SOCE). However, no direct evidence has been obtained about these signaling pathways in odontoblasts. In this study, we investigate the characteristics of the SOCE and IP(3)-mediated Ca(2+) mobilizations in rat odontoblasts using fura-2 microfluorometry and a nystatin-perforated patch-clamp technique. In the absence of extracellular Ca(2+) ([Ca(2+)](o)), thapsigargin (TG) evoked a transient rise in intracellular Ca(2+) concentration ([Ca(2+)](i)). After TG treatment to deplete the store, the subsequent application of Ca(2+) resulted in a rapid rise in [Ca(2+)](i) caused by SOCE. In the absence of TG treatment, no SOCE was evoked. The Ca(2+) influx was dependent on [Ca(2+)](o). (K(D) = 1.29 mM) and was blocked by an IP(3) receptor inhibitor, 2-aminoethoxydiphenyl borate (2-APB), as well as La(3+) in a concentration-dependent manner (IC(50) = 26 muM). In TG-treated cells, an elevation of [Ca(2+)](o) from 0 to 2.5 mM elicited an inwardly rectifying current at hyperpolarizing potentials with a positive reversal potential. The currents were selective for Ca(2+) over the other divalent cations (Ca(2+) > Ba(2+) > Sr(2+) much greater than Mn(2+)). In the absence of [Ca(2+)](i), carbachol, bradykinin, and 2-methylthioadenosine 5'triphosphate activated Ca(2+) release from the store; these were inhibited by 2-APB. These results indicate that odontoblasts possessed Ca(2+) signaling pathways through the activation of store-operated Ca(2+) channels by the depletion of intracellular Ca(2+) stores and through the IP(3)-induced Ca(2+) release activated by PLC-coupled receptors.