Transport Functions of Ectoderm Epithelial Cells Forming Dental Enamel

The development of enamel encapsulates fundamental cellular processes associated with the intricate life stages of the ectodermal epithelial cells known as ameloblasts that regulate its growth. Ameloblasts are tall and narrow cells with reversed polarity and advance as a front producing the enamel matrix with unique properties. Following the development of the full thickness of the enamel, ameloblasts then switch their elongated morphology becoming a cell with the appearance of transporting epithelium. Enamel is then mineralized to reach a mineral content of ~96% by weight. The last 10 years have seen a surge in studies aiming to identify the transport machinery used by ameloblasts to generate such mineralization levels. While the majority of the mineral content of enamel is dominated by Ca2+ (36%) and Pi (18%), there are a number of other important contributors to the development of the carbonated hydroxyapatite enamel crystals, including HCO3–, Cl–, Mg2+, and others. Yet there is a clear interplay among the channels, pumps, exchangers, and transporters involved in ion transport in ameloblasts. Part of these connections arise from the need to ensure an intensification of mineral growth alongside careful monitoring of extracellular pH. Although the molecular components of transporting ameloblasts are emerging, much remains to be done. Here, we describe the current model for ion transport by ameloblasts.