Regulation of Ca<inf>V</inf>3.1 channels by glucocorticoids

The activity of low voltage-activated Ca2+(CaV3) channels is tightly coupled to neurotransmitter and hormone secretion. Previous studies have shown that CaV3 channels are regulated by glucocorticoids (GCs), though the mechanism underlying channel regulation remains unclear. Here, using the pituitary GH3cell line as a model, we investigated whether CaV3 channel expression is under the control of GCs, and if their actions are mediated by transcriptional and/or post-transcriptional mechanisms. RT-PCR and western blot analyses showed that CaV3.1 but not CaV3.2 and CaV3.3 channels is expressed in the GH3cells, and patch clamp recordings confirmed that Ca2+currents through low voltage-activated channels were decreased after chronic treatment with GCs. Consistent with this, total plasma membrane expression of CaV3.1 protein as analyzed by cell-surface biotinylation assays and semi-quantitative western blotting was also down-regulated, while quantitative real-time RT-PCR analysis revealed a significant decrease of CaV3.1 mRNA expression in the treated cells. In contrast, patch-clamp recordings on HEK-293 cells stably expressing recombinant CaV3.1 channels showed that Ca2+currents were not affected by GC treatment. These results suggest that decreased transcription is a likely mechanism to explain the inhibitory actions of GCs on the functional expression of native CaV3.1 channels. © 2009 Springer Science+Business Media, LLC.