CALCIUM IS AN EQUIPOTENT STIMULATOR OF STANNIOCALCIN SECRETION IN FRESH-WATER AND SEAWATER SALMON

Stanniocalcin (STC) is a calcium- and phosphate-regulating hormone pro duced by the corpuscles of Stannius in fishes. A rise in ion calcium ( Ca2+) levels is the principal stimulus for secretion, and the hormone acts on the gills, gut, and kidneys to restore normocalcemia. The STC- producing cells in marine fishes are metabolically more active and sec rete more hormone than those in freshwater fishes, which has been attr ibuted to the higher calcium content of seawater placing a greater bur den on the organ systems governing Ca2+ homeostasis. In this study we have addressed the question of whether or not the STC cells in marine fishes are more sensitive to Ca2+, by comparing the secretagogic effec ts of Ca2+ in freshwater- and seawater-adapted coho salmon. The result s showed that the STC cells were equally Ca2+-sensitive in the two gro ups. Therefore, in spite of the fact that the STC cells are more activ e in marine fishes this requires no apparent adjustment in cellular se nsitivity to calcium. (C) 1998 Academic Press.