For a long time it was thought that the corpuscles of Stannius (CS) of holostean and teleostean fishes produce a single hormone reducing Ca2+ influx from the water via the gills. We here present data showing that two separate bioactive principles are present in the CS: stanniocalcin (STC), a 56 kDa glycoprotein, and teleocalcin (TC), a 3 kDa glycopeptide. STC indeed inhibits Ca2+ influx (as reported many times before) but does not affect the Ca2+- and Mg2+-dependent phosphatase activity located in the gill plasma membrane. TC does not affect Ca2+ influx but inhibits the Ca2+- and Mg2+-dependent phosphatase activity. Thus, the Ca2+- and Mg2+-dependent phosphatase activity appears not to be involved in transbranchial Ca2+ transport. We conclude that STC is the pivotal calcium-regulating hormone in fish and that TC has an as yet unidentified role in gill physiology through its phosphatase-reducing activity.

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