Objective: A highly selective, amiloride-sensitive epithelial sodium channel (ENaC) mediates active Na⁺ re-absorption through the apical membrane of absorbing epithelial cells as well as non-transporting epithelia. ENaC is composed of different homologous proteins, denoted as α, β, and γ subunits. The present study was undertaken to reveal the expression of ENaC subunits and their localization by immunohistochemistry and in situ hybridization in the rat incisor enamel organ. Materials and Methods: Paraffin sections of the incisors obtained from 8-week-old Wistar rats were processed for immunohistochemistry and in situ hybridization for ENaC subunits. Results: The rat enamel organ expressed ENaC α, β, and γ subunit mRNAs. In the maturation zone, which includes both papillary and ameloblast layers, we morphologically classified the enamel organ as ruffle-ended ameloblast area (RA), smooth-ended ameloblast area (SA), and maturation zone transitional area (MTA), which are group of cells immediately preceding the SA. The expression of ENaC subunits in the enamel organ considerably differed between RA and SA. The immuno-intensity and mRNA signal expression in RA was significantly greater than in SA. Furthermore, the reactions varied in intensity within RA with the cells towards the incisal end showing significantly increased immunoreactions. As the maturation zone progresses to MTA, a progressive increase that peaked at the MTA was observed. Subsequently, the expression pattern significantly decreased at SA. Overall, the ENaC labeling pattern exhibited a periodic change at the maturation stage in the rat enamel organ. Conclusion: Our results demonstrated a cyclic expression of ENaC subunits in rat ameloblasts and papillary layer cells at maturation zone, suggesting ENaC participation in enamel maturation presumably by modulation of Na⁺ ion transport.

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