EFFECTS OF CALCIUM AGONISTS ON VITELLOGENIN INDUCTION BY ESTRADIOL-17-BETA IN PRIMARY HEPATOCYTE CULTURE IN THE RAINBOW-TROUT ONCORHYNCHUS-MYKISS

Effects of calcium agonists (A23187, caffein, ryanodine, and thapsigar gin) on estradiol-induced vitellogenin (VTG) induction were examined i n primary hepatocyte culture in the rainbow trout Oncorhynchus mykiss. These agonists are effective in depleting calcium in various calcium stores. Hepatocytes were precultured for 2 days and then estradiol-17 beta (E-2, 2 x 10(-6)M) and the agonists were simultaneously added to the incubation medium. The hepatocytes were cultured for 7 more days a nd then spent medium was analyzed by SDS-PAGE. The relative rate of VT G production was evaluated by measuring the integrated optical density of the main VTG band and was expressed as the percentage of VTG to to tal proteins including the VTG. The addition of A23187 (10(-7)similar to 10(-6)M), caffein (10(-4)similar to 10(-2)M) or thapsigargin (10(-7 )similar to 10(-6)M) to the incubation medium specifically reduced VTG production by hepatocytes in a concentration-dependent way. Ryanodine also reduced the production to about 60% of the control at a concentr ation of 10(-4)M. These results suggest that the synthesis of VTG is m ore susceptible to intracellular sequestered calcium, at least to calc ium in the endoplasmic reticulum, than are other hepatocyte-derived pr oteins in rainbow trout.