Subcellular co-localization and co-variations of two vitamin D-dependent proteins in rat ameloblasts

The immunocytochemical patterns of calbindin-D9k (CaBP 9k) and calbindin-D28k (CaBP 28k) were compared by light and electron microscopy throughout amelogenesis. Labelling on serial sections and co-localization of CaBPs confirmed that the two proteins were restricted to a single cell type, the ameloblasts. Their quantity increased during presecretion, was stable during secretion and alternately high and low during the cyclic modulation of ameloblasts which occurs during maturation. Ruffle-ended ameloblasts contained the highest apparent concentration. Investigations with several fixatives indicated that the CaBPs were present in the cytosol and the nucleus, although there were slight differences with various fixatives by light microscopy. Their concentrations in these compartments varied in parallel throughout amelogenesis. However, mitochondria contained only immunoreactive CaBP 9k. While the distribution of CaBP 9k in zones containing Golgi apparatus and rough endoplasmic reticulum was similar, CaBP 28k concentration has, in another paper, been shown to be higher near the rough endoplasmic reticulum.