Steroidogenesis in isolated adrenal cells: excitation by calcium

Calcium salts were found to replace ACTH in inducing steroidogenesis in isolated adrenocortical cells from rats. This Ca-specific stimulation occurred when the cation was presented to the cells in the presence of phosphate and carbonate as a counter-ions under conditions which favoured the formation of colloidal calcium. Colloid generation and stabilization was facilitated by the use of calcium buffers and gelatin. Stable soluble or sparingly soluble calcium complexes were inactive. The preparation of cells and metastable calcium solutions is described in detail. The Ca trigger was sensitive to Ca deprivation or inhibitors of Ca transport and could be replced by Sr. The relative role of Ca and cyclic AMP as second messengers is discussed.