Immunocytochemical Localization of Na+,K+-ATPase in the Calcium-transporting Sternal Epithelium of the Terrestrial IsopodPorcellio scaberL. (Crustacea)

Abstract

Terrestrial isopods store large amounts of calcium carbonate between the epithelium and the old cuticle of the first four anterior sternites before molt. During the formation of these sternal CaCO3deposits, large amounts of calcium are transported across the anterior sternal epithelium from the base to the apical side of the integument, and in the reverse direction during resorption of the deposit. A monoclonal antibody against the avian α-subunit of Na+,K+-ATPase was used to localize Na+,K+-ATPase in the anterior and the posterior sternal epithelium of Porcellio scaber. Semithin cryosections 0.5 μm thick were used for immunofluorescence microscopy and ultrathin cryosections for immunogold electron microscopy. The Na+,K+-ATPase was localized in the basolateral plasma membrane of the posterior and anterior sternal epithelium. The apical plasma membrane, including cytoplasmic extensions into the newly secreted cuticle, was virtually devoid of the enzyme. This pattern of immunolocalization was not affected by the direction of transepithelial calcium transport associated with the deposition and resorption phases of the molt cycle.(J Histochem Cytochem 45:437–446, 1997)