Localization of Plasma Membrane Ca2+ Pump mRNA and Protein in Human Ameloblasts by In Situ Hybridization and Immunohistochemistry

The distribution of the plasma membrane Ca²⁺-pump (PMCA) proteins in human ameloblasts was examined immunohistochemically using monoclonal antibodies JA8 and 5F10. Further, the distribution of mRNA transcripts derived from two PMCA genes, PMCA-1 and PMCA-4 was examined using in situ hybridization. In rats, the PMCA-1 gene is purported to code for PMCA proteins with a role in maintaining the intracellular Ca²⁺ levels in nonepithelial cells. Other genes including the PMCA-4 gene may code for PMCA proteins characteristic of Ca²⁺ transporting epithelia. The present results show immunohistochemical staining in the Tomes processes and plasma membranes of human ameloblasts. Our studies also demonstrate a gradation of expression of the PMCA-1 and PMCA-4 mRNA transcripts which parallels the onset and progression of enamel mineralization.

These studies suggest that PMCA proteins in human ameloblasts may function both in intracellular Ca²⁺ homeostasis and in regulating the vectorial Ca²⁺ influx into mineralizing enamel.