Degranulation of the stannius corpuscles of coho salmon ( Oncorhynchus kisutch) in response to lonic changes in vitro

Abstract

Stannius corpuscles of the coho salmon, Oncorhynchus kisutch, were maintained in organ culture in defined media containing various concentrations of calcium. Standard [Ca 2+] (1.5 m M) or lower levels do not induce degranulation. Degranulation and concomitant increase in rough-surfaced endoplasmic reticulum and Golgi systems were seen after high [Ca 2+] (3 and 6 m M) in both cell types beginning as early as 2 hr after the start of incubation. Degranulation occurred as a result of exocytosis. Ethylenediamine tetraacetic acid blocked the effect of high [Ca 2+]. [Mg 2+] had no effect whereas [Sr 2+] had an effect if some Ca 2+ was present. The calcium ionophore, A23187, at concentrations above 10 −5 M in the presence of standard [Ca 2+], induced exocytosis in both cell types. Low [Na +] (50 and 100 m M) with Ca 2+ present caused moderate to high degranulation and high [Na +] (225 m M) caused moderate degranulation with a [Ca 2+] (3 m M) that typically caused high degranulation. These results indicate that the secretory activity of the cells of the Stannius corpuscles may be directly affected by plasma ion levels, especially Ca 2+.