Immunocytological localization of 1,25-dihydroxyvitamin D₃-like molecules and their receptors in a calcium-transporting epithelium of a crustacean

For the first time, immunoreactivity to 1,25(OH)₂D₃-like molecules and their receptors has been investigated in a calcium transporting epithelium of a crustacean, Orchestia, using vertebrate antisera on ultrathin cryosections of posterior caeca previously fixed in glutaraldehyde, then postfixed in osmium tetroxide. Both immunoreactivities were located mainly in the nuclei of epithelial cells. Quantitative differences in 1,25(OH)₂D₃-like immunoreactivity were noticed from one stage of the molt cycle to another. These results, together with other data, contribute to evidence that immunoreactive 1,25(OH)₂D₃-like molecules may be involved in the regulatory processes of calcium metabolism in this terrestrial crustacean and suggest an involvement of these substances in the regulation of calcium movements in the posterior caeca.