Effects of membrane-active compounds on dexamethasone binding to the glucocorticoid receptor in intact cells.

In intact rat hepatoma (HTC) cells, the binding of dexamethasone to the glucocorticoid receptor is inhibited by the calcium ionophore A23187. This effect involves both nuclear-bound and cytoplasmic receptor. Indirect evidence suggests that the inhibition requires intracellular calcium stores. Exposure of the cells to concanavalin A also inhibits dexamethasone binding. Based on earlier work in cell-free systems, it is proposed that membrane-active agents could modulate glucocorticoid hormone action at the receptor level through fluctuations in intracellular free calcium.