Adrenocorticotropin induces calcium oscillations in adrenal fasciculata cells: single cell imaging.

With fluorescence microscopic imaging, we have demonstrated that the Ca2+ signaling occurred in individual Calcium Green-1 loaded bovine adrenal fasciculata cells upon stimulation with adrenocorticotropin (ACTH) at physiological concentration of 0.1-100 pM. We observed three patterns of Ca2+ signaling which were Ca2+ oscillations (33%), step-like increase in Ca2+ concentration (10%), and Ca2+ oscillations superimposed on step-like increase in Ca2+ (57%). The oscillation in intracellular Ca2+ concentration occurred with a frequency around 0.04 Hz. When Ca2+ signaling upon ACTH stimulation was inhibited by the treatment with EGTA, the corticoid production was considerably suppressed. The results suggest that the Ca2+ signaling is a probable candidate of the second messenger for ACTH-induced steroid hormone synthesis in zona fasciculata cells.