Glucocorticoids Rapidly Modulate Ca1.2-Mediated Calcium Signals through Kv2.1 Channel Clusters in Hippocampal Neurons.

The precise regulation of Ca signals plays a crucial role in the physiological functions of neurons. Here, we investigated the rapid effect of glucocorticoids on Ca signals in cultured hippocampal neurons from both female and male rats. In cultured hippocampal neurons, glucocorticoids inhibited the spontaneous somatic Ca spikes generated by Kv2.1-organized Ca microdomains. Furthermore, glucocorticoids rapidly reduced the cell surface expressions of Kv2.1 and Ca1.2 channels in hippocampal neurons. In HEK293 cells transfected with Kv2.1 alone, glucocorticoids significantly reduced the surface expression of Kv2.1 with little effect on K currents. In HEK293 cells transfected with Ca1.2 alone, glucocorticoids inhibited Ca1.2 currents but had no effect on the cell surface expression of Ca1.2. Notably, in the presence of wild-type Kv2.1, glucocorticoids caused a decrease in the surface expression of Ca1.2 channels in HEK293 cells. However, this effect was not observed in the presence of nonclustering Kv2.1S586A mutant channels. Live-cell imaging showed that glucocorticoids rapidly decreased Kv2.1 clusters on the plasma membrane. Correspondingly, Western blot results indicated a significant increase in the cytoplasmic level of Kv2.1, suggesting the endocytosis of Kv2.1 clusters. Glucocorticoids rapidly decreased the intracellular cAMP concentration and the phosphorylation level of PKA in hippocampal neurons. The PKA inhibitor H89 mimicked the effect of glucocorticoids on Kv2.1, while the PKA agonist forskolin abrogated the effect. In conclusion, glucocorticoids rapidly suppress Ca1.2-mediated Ca signals in hippocampal neurons by promoting the endocytosis of Kv2.1 channel clusters through reducing PKA activity.