Ultrastructural study of the Ca2+-dependent ATPase activity in rat adenohypophyseal cells.

Ca-dependent ATPase activity in the rat anterior pituitary was demonstrated in 50-microns tissue slices of aldehyde-fixed tissue with the medium of Takano et al. (Cell Tissue Res. 243:91. 1986).--The outer surface of the plasma membrane of the parenchymal as well as the folliculo-stellate cells was lined with lead precipitate. The reaction deposit was particularly well localized in intercellular spaces both between two parenchymal cells, and between a parenchymal and a folliculo-stellate cell. A fine reaction deposit was also seen in the endoplasmic reticulum and Golgi apparatus of some parenchymal cells. Elimination of Ca2+ from the tissue and the substrate medium drastically reduced the amount of reaction product. If ATP was omitted or replaced by sodium beta-glycerophosphate, no reaction product was seen. Changing the Ca2+ concentration or addition of Mg2+ to the standard medium caused a decrease in reaction intensity. Substitution of Mg2+ for Ca2+ resulted, again in well-localized lead deposition which we attribute to the activity of another enzyme. We suggest that the activity we described in the membrane of glandular cells may correspond to the enzyme involved in the long-term regulation of intracellular Ca2+ level.