Calcium is an equipotent stimulator of stanniocalcin secretion in freshwater and seawater salmon

Stanniocalcin (STC) is a calcium- and phosphate-regulating hormone produced 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 secrete more hormone than those in freshwater fishes, which has been attributed to the higher calcium content of seawater placing a greater burden 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 effects of Ca2+ in freshwater- and seawater-adapted coho salmon. The results showed that the STC cells were equally Ca(2+)-sensitive in the two groups. Therefore, in spite of the fact that the STC cells are more active in marine fishes this requires no apparent adjustment in cellular sensitivity to calcium.