Adrenocorticoid receptors in C6 glioma cells: effects on cell growth.

Rat C6 glioma cells contain two receptors for adrenocorticoids--the predominant glucocorticoid receptor and low densities of the Type I corticosteroid (mineralocorticoid) receptor. Nanomolar concentrations of deoxycorticosterone, corticosterone and aldosterone, which fully occupy Type I receptors, produced a slight stimulatory effect on C6 cell growth in serum-free media. However, spironolactone, a Type I receptor antagonist, and pregnenolone, which does not bind to Type I receptors, had similar effects. Therefore, the slight growth stimulation produced by low steroid concentrations is not mediated by Type I or glucocorticoid receptors, but may be due to an effect on cell membrane properties or other receptor-independent action. Occupation of glucocorticoid receptors by higher concentrations of corticosteroids inhibited C6 cell growth.