Directional Ca²⁺ transport via sodium/calcium exchangers, NCX3, in rat odontoblasts during dentinogenesis.

Abstract

Ca²⁺ is essential for the signal transduction pathways. We have previously demonstrated several Ca²⁺ mobilization mechanisms in odontoblasts such as; IP₃-induced Ca²⁺ release by PLC-coupled receptor activities, depolarization mediated Ca²⁺ mobilization and Ca²⁺ influx via store-operated Ca²⁺ channels. The [Ca²⁺]i levels are tightly regulated by the Ca²⁺ extrusion system including Na⁺/ Ca²⁺ exchangers (NCX) in the plasma membrane, however, no direct functional evidence has been obtained Na⁺/Ca²⁺ exchange pathway in odontoblasts. In this study, we investigated presence and functional characteristics of NCX in odontoblasts. NCX activities were measured with a fura-2 and patch-clamp technique. For Immunohistochemistry, cryostat sections were incubated with monoclonal antibodies against NCX, and labeled using fluorescent secondary antibodies. The reverse and forward exchange showed dependence on extracellular Ca²⁺ and Na⁺ concentrations, respectively. In addition, reverse exchange was blocked by an NCX inhibitor (KB-R7943) in a concentration dependent manner, while was not inhibited by SEA0400. NCX immunoreaction was observed on the odontoblast plasma membranes. These results indicate that odontoblasts express plasma membrane NCX3 which may operate Ca²⁺ extrusion after accelerated Ca²⁺ signals via store-operated Ca²⁺ channels during dentinogenesis. [J Physiol Sci. 2007;57 Suppl:S76]