Department of Dental Pathology, Operative Dentistry, and Endodontics, Aarhus University, Aarhus, Denmark.
Am J Physiol Cell Physiol. 2010 Dec;299(6):C1299-307. doi: 10.1152/ajpcell.00218.2010. Epub 2010 Sep 15.
Mature enamel consists of densely packed and highly organized large hydroxyapatite crystals. The molecular machinery responsible for the formation of fully matured enamel is poorly described but appears to involve oscillative pH changes at the enamel surface. We conducted an immunohistochemical investigation of selected transporters and related proteins in the multilayered rat incisor enamel organ. Connexin 43 (Cx-43) is found in papillary cells and ameloblasts, whereas Na(+)-K(+)-ATPase is heavily expressed during maturation in the papillary cell layer only. Given the distribution of Cx-43 channels and Na(+)-K(+)-ATPase, we suggest that ameloblasts and the papillary cell layer act as a functional syncytium. During enamel maturation ameloblasts undergo repetitive cycles of modulation between ruffle-ended (RA) and smooth-ended (SA) ameloblast morphologies. Carbonic anhydrase II and vacuolar H(+)-ATPase are expressed simultaneously at the beginning of the maturation stage in RA cells. The proton pumps are present in the ruffled border of RA and appear to be internalized during the SA stage. Both papillary cells and ameloblasts express plasma membrane acid/base transporters (AE2, NBC, and NHE1). AE2 and NHE1 change position relative to the enamel surface as localization of the tight junctions changes during ameloblast modulation cycles. We suggest that the concerted action of the papillary cell layer and the modulating ameloblasts regulates the enamel microenvironment, resulting in oscillating pH fluctuations. The pH fluctuations at the enamel surface may be required to keep intercrystalline spaces open in the surface layers of the enamel, enabling degraded enamel matrix proteins to be removed while hydroxyapatite crystals grow as a result of influx of calcium and phosphate ions.
成熟的牙釉质由密集排列且高度有序的大羟基磷灰石晶体组成。负责形成完全成熟牙釉质的分子机制描述得还不完善，但似乎涉及牙釉质表面的振荡 pH 变化。我们对多层大鼠切牙牙釉质器官中的选定转运体和相关蛋白进行了免疫组织化学研究。连接蛋白 43（Cx-43）存在于乳突细胞和成釉细胞中，而 Na(+)-K(+)-ATP 酶在乳突细胞层的成熟过程中大量表达。鉴于 Cx-43 通道和 Na(+)-K(+)-ATP 酶的分布，我们推测成釉细胞和乳突细胞层作为一个功能合胞体发挥作用。在牙釉质成熟过程中，成釉细胞经历了波纹状末端（RA）和光滑末端（SA）成釉细胞形态之间的反复调节循环。碳酸酐酶 II 和液泡 H(+)-ATP 酶在 RA 细胞的成熟阶段开始时同时表达。质子泵存在于 RA 的皱襞边缘，在 SA 阶段似乎被内化。乳突细胞和成釉细胞均表达质膜酸碱转运体（AE2、NBC 和 NHE1）。AE2 和 NHE1 相对于牙釉质表面的位置随着紧密连接在成釉细胞调节循环中的定位变化而变化。我们认为，乳突细胞层和调节中的成釉细胞的协同作用调节牙釉质微环境，导致 pH 振荡波动。牙釉质表面的 pH 波动可能是必需的，以保持牙釉质表面层的晶间空间开放，从而使降解的牙釉质基质蛋白能够在钙和磷酸盐离子流入时被去除，同时羟基磷灰石晶体生长。
