The role of ether-a-go-go-related gene K+ channels in glucocorticoid inhibition of adrenocorticotropin release by rat pituitary cells

The present study investigated the role of K+ channels in the inhibitory effect of glucocorticoid on adrenocorticotropin (ACTH) release induced by corticotropin-releasing hormone (CRH) using cultured rat anterior pituitary cells. Apamin and charybdotoxin (CTX) did not have a significant effect on ACTH release induced by CRH (1 nM). Tetraethylammonium (TEA), a broad spectrum K+ channel blocker, increased the ACTH response to CRH only at the highest concentration (10 mM). The exposure to 100 nM corticosterone for 60 min inhibited the CRH-induced ACTH release. Neither TEA, apamin, nor CTX affected the inhibitory effect of corticosterone. In contrast, astemizole (Ast) and E-4031, ether-a-go-go-related gene (erg) K+ channel blockers, abolished the inhibitory effect of corticosterone on CRH-induced ACTH release (1.25 ± 0.10 vs. 1.45 ± 0.11 ng/well at 10 μM Ast, p > 0.05, 1.71 ± 0.16 vs. 1.91 ± 0.32 ng/well at 10 μM E-4031, p > 0.05, vehicle vs. corticosterone). RT-PCR demonstrated all three subtypes of rat-erg mRNAs in the pituitary and corticosterone increased only erg1 mRNA up to 2.47 ± 0.54 fold. In conclusion, erg K+ channels were up-regulated by glucocorticoid, and have indispensable roles in delayed glucocorticoid inhibition of CRH-induced ACTH release by rat pituitary cells.