INDICATIONS FOR 2 BIOACTIVE PRINCIPLES IN THE CORPUSCLES OF STANNIUS

For a long time it was thought that the corpuscles of Stannius (CS) of holostean and telcostean fishes produce a single hormone reducing Ca2 + influx from the water via the gills. We here present data showing th at two separate bioactive principles are present in the CS: stanniocal cin (STC), a 56 kDa glycoprotein, and teleocalcin (TC), a 3 kDa glycop eptide. STC indeed inhibits Ca2+ influx (as reported many times before ) but does not affect the Ca2+- and Mg2+-dependent phosphatase activit y 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 in volved in transbranchial Ca2+ transport. We conclude that STC is the p ivotal calcium-regulating hormone in fish and that TC has an as yet un identified role in gill physiology through its phosphatase-reducing ac tivity.