Expression of Ca 2+-ATPase and Na +/Ca 2+-exchanger is upregulated during epithelial Ca 2+ transport in hypodermal cells of the isopod Porcellio scaber

Abstract

It is thought that a plasma membrane Ca 2+-transport ATPase (PMCA) and a Na +/Ca 2+-exchange (NCE) mechanism are involved in epithelial Ca 2+ transport (ECT) in a variety of crustacean epithelia. The sternal epithelium of the terrestrial isopod Porcellio scaber was used as a model for the analysis of Ca 2+-extrusion mechanisms in the hypodermal epithelium. Using RT-PCR, we amplified a cDNA fragment of 1173 bp that encodes a protein sequence possessing 72% identity to the PMCA from Drosophila melanogaster and a cDNA fragment of 791 bp encoding a protein sequence with 50% identity to the NCE from Loligo opalescens. Semiquantitative RT-PCR revealed that the expression of both mRNAs increases from the non-Ca 2+-transporting condition to the stages of CaCO 3 deposit formation and degradation. During Ca 2+-transporting stages, the expression of PMCA and NCE was larger in the anterior sternal epithelium (ASE) than in the posterior sternal epithelium (PSE). The results demonstrate for the first time the expression of a PMCA and a NCE in the hypodermal epithelium of a crustacean and indicate a contribution of these transport mechanisms in ECT.