Figure 8.
Major activities of maturation stage ameloblasts. (A) Calcium (Ca2+) and phosphate (H2PO4- and HPO42-) ions are transported and add to the width and thickness of existing calcium hydroxyapatite crystals generating hydrogen ions (H+). (B) Enamel proteins are cleaved by kallikrein (KLK4) and reabsorbed into the cells, possibly with the assistance of WDR72. (C) Magnesium ions (Mg2+) are potentially removed from the matrix by CNNM4. (D) Carbonic anhydrase II (CA2) catalyzes the combination of carbon dioxide (CO2) and water (H2O) to form a bicarbonate ion (HCO3-) and a hydrogen ion. The H+ is removed from the cell, possibly by the action of a sodium (Na+) and hydrogen ion exchanger (NHE) on the proximal membrane. The bicarbonate ion is transported into the matrix by exchanging it for a chloride ion (Cl-) by anion exchanger 2 (AE2). The cystic fibrosis transmembrane regulator protein may facilitate this exchange by transporting Cl- out of the cell and into the matrix. (E) Carbonic anhydrase VI (CA6) catalyzes the combination of bicarbonate and a hydrogen ion generated by hydroxyapatite formation to form carbon dioxide and water. ODAM and amelotin (AMTN) are components of the basal lamina along the distal membrane of ameloblasts throughout the maturation stage. No attempt has been made to distinguish between the activities of ruffle-ended and smooth ended ameloblasts. The proximal side of the ameloblast is at the top; the distal side is at the bottom. The enamel rod images are from Nanci (2003).