DEXAMETHASONE RAPIDLY INCREASES CALCIUM-CHANNEL SUBUNIT MESSENGER-RNAEXPRESSION AND HIGH VOLTAGE-ACTIVATED CALCIUM CURRENT IN CLONAL PITUITARY-CELLS

Glucocorticoid hormones increase voltage-gated Ca2+ current density in clonal pituitary cells. To test whether these steroids might stimulat e expression of Ca2+ channel genes, messenger RNase protection assays were used to measure alpha(1C) and alpha(1D) RNAs that encode pore-for ming subunits of L-type Ca2+ channels. We show here that dexamethasone rapidly increases alpha(1C) messenger RNA expression without affectin g alpha(1D) messenger RNA level. This up-regulation of channel messeng er RNA is also produced by natural glucocorticoids and is blocked by t he glucocorticoid antagonist Ru48386. The up-regulation of the channel subunit messenger RNA expression is associated with an increase in hi gh voltage-activated Ca2+ current density. Thus, glucocorticoids may p roduce a long-term effect on Ca2+ homeostasis in clonal pituitary cell s by differentially regulating expression of Ca2+ channel subunit gene s.