Sodium-Calcium Exchangers in Rat Ameloblasts

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Although the central role of ameloblasts in synthesis and resorption of enamel matrix proteins during amelogenesis is well documented, the Ca²⁺-transport/extrusion mechanism remains to be fully elucidated. To clarify Ca²⁺-transport in rat ameloblasts, we investigated expression and localization of Na⁺-Ca²⁺ exchanger (NCX) isoforms and the functional characteristics of their ion transporting/pharmacological properties. RT-PCR and immunohistochemical analyses revealed expression of NCX1 and NCX3 in ameloblasts, localized in the apical membrane. In patch-clamp recordings, Ca²⁺ efflux by Na⁺-Ca²⁺ exchange showed dependence on external Na⁺. Ca²⁺ influx by Na⁺-Ca²⁺ exchange, measured by fura-2 fluorescence, showed dependence on extracellular Ca²⁺ concentration, and it was blocked by NCX inhibitors KB-R7943, SEA0400, and SN-6. These results showed significant expression of NCX1 and NCX3 in ameloblasts, indicating their involvement in the directional Ca²⁺ extrusion pathway from cells to the enamel mineralizing front.