エナメル芽細胞の直接的なCa²⁺輸送はNCX1・3によって仲介される

抄録

Ameloblasts are the cells responsible for enamel formation (amelogenesis). Although the central role of ameloblasts in synthesis and resorption of enamel matrix proteins has been well documented, Ca²⁺ transport mechanisms during amelogenesis have not been fully elucidated. In order to clarify Ca²⁺ transport mechanisms in rat ameloblasts, we investigated presence and functional characteristics of Na⁺/Ca²⁺ exchangers (NCX). NCX activities were measured with fura-2 and patch clamp technique. RT-PCR analysis was performed to identify the presence of transcripts for the NCX isoforms. For Immunohistochemistry, cryostat sections were prepared by slicing of the mandible including incisor. These sections were incubated with monoclonal antibodies against NCX, and labeled using fluorescent secondary antibodies. Ca²⁺ influx via reverse exchange showed dependence on extracellular Ca²⁺ concentration (Kd₅₀ = 0.25 mM), and was blocked by a NCX inhibitor, KB-R 7943, in a concentration dependent manner (IC₅₀ = 4.34 μM). Ca²⁺ efflux via forward exchange showed dependence on extracellular Na⁺ concentration. RT-PCR analysis revealed expression of NCX1 and 3 mRNA in ameloblasts. Immunohistochemistry showed localization of NCX on the ameloblast plasma membranes. Our results indicate significant expression of NCX in ameloblasts. Na⁺/Ca²⁺ exchangers may serve as a directional Ca²⁺ transporting pathway to the enamel mineralizing front from circulation. [J Physiol Sci. 2007;57 Suppl:S134]