Evidence for Bicarbonate Secretion by Ameloblasts in a Novel Cellular Model

Formation and growth of hydroxyapatite crystals during amelogenesis generate a large number of protons that must be neutralized, presumably by HCO3− ions transported from ameloblasts into the developing enamel matrix. Ameloblasts express a number of transporters and channels known to be involved in HCO3− transport in other epithelia. However, to date, there is no functional evidence for HCO3− transport in these cells. To address questions related to HCO3− export from ameloblasts, we have developed a polarized 2-dimensional culture system for HAT-7 cells, a rat cell line of ameloblast origin. HAT-7 cells were seeded onto Transwell permeable filters. Transepithelial resistance was measured as a function of time, and the expression of transporters and tight junction proteins was investigated by conventional and quantitative reverse transcription polymerase chain reaction. Intracellular pH regulation and HCO3− transport were assessed by microfluorometry. HAT-7 cells formed epithelial layers with measureable t...