Junctional proteins and Ca2+ transport in the rat odontoblast-like cell line MRPC-1

A transcellular bulk flow of Ca2+ ions through the odontoblast layer is of central importance during dentinogenesis. For this, specialized mechanisms may exist, which by a concerted action, gate Ca2+ into the proximal end of the cells and extrude the ions towards the mineralization front. To elucida te these mechanisms, an in vitro model would be useful. Mature odontoblasts are, however, post-mitotic cells and cannot be propagated in cell culture. The aim of the present study was, therefore, to characterize the odontobla st-like rat cell line MRPC-1(1) with regard to transcellular Ca2+ transport , barrier function, and intercellular junctions when cultured on membranes in Transwell chambers. The MRPC-1 cells grew as epithelial-like cells in a continuous bilayer separated by a thin collagenous matrix and with intercel lular junctional complexes. They exhibited properties of a low-resistance e pithelium, maintained a Ca2+-dependent diffusion barrier, and exhibited a f unctional diversity between the two cell layers. MRPC-1 cells expressed ZO- 1. occludin, E-l and N-cadherins in addition to alpha-, beta-, gamma- and p 120(cat) catenins, thereby demonstrating some traits in common with, but al so differences from. epithelial cells and major differences from fibroblast s. The transcellular Ca2+ flux was inhibitable by nifedipine unidirectional ly, giving evidence for an active intracellular Ca2+ transport through volt age-gated channels of the L-type. Similarities with native odontoblasts ind icate that MRPC-1 cells may be useful for in vitro studies of transcellular Ca2+ transport mechanisms of importance for the calcification process.