Expression and polarity reversal of V-type H⁺-ATPase during the mineralization-demineralization cycle in Porcellio scaber sternal epithelial cells

The formation and resorption of CaCO₃ by epithelial cell layers require epithelial transport of protons. We used the anterior sternal epithelium of the terrestrial isopod Porcellio scaber as a model to study the expression pattern and immunolocalization of a V-type H⁺-ATPase during the mineralization and demineralization of intermittent CaCO₃ deposits. Semiquantitative RT-PCR revealed that the expression of the V-type H ⁺-ATPase increases from non Ca²⁺-transporting control stages to the stages of CaCO₃ deposit formation and resorption. In the Ca²⁺-transporting stages the expression was larger in the anterior than in the posterior sternal epithelium, which is not involved in deposit formation and transports just moderate amounts of CaCO₃. Immunocytochemistry of the B-subunit of the V-type H⁺-ATPase in the anterior sternal epithelium reveals an increase in the abundance of the protein within the basolateral membrane, from undetectable to strong signals in the control stage to the stages of CaCO₃ deposit formation, respectively. From the stage of CaCO₃ deposit formation to that of CaCO ₃ resorption the signal decreased within the basolateral plasma membrane and increased within the apical plasma membrane. For the first time the results indicate a contribution of a V-type H⁺-ATPase to CaCO ₃ deposition and a reversal of its polarity from the basolateral to the apical plasma membrane compartment within the same cells.