Sustained depolarization decreases calcium/calmodulin-dependent protein kinase II activity and gene expression in dopamine neurons

Abstract

Altered gene expression mediated by calcium/calmodulin-dependent protein kinase II (CaMKII) and other intracellular signaling molecules plays an important role in activity-dependent neuroplasticity. We discovered that sustained depolarization induced by KCl, a commonly used paradigm for studying activity-dependent gene expression, surprisingly caused a decrease in CaMKII activity in rat mesencephalic dopamine neurons. This decrease in CaMKII activity, after 2 days of depolarization, occurred in the presence of a continued elevation in intracellular calcium concentration. An increase in calyculin-sensitive phosphatase activity was at least partly responsible for the decrease in CaMKII activity. Phosphatase assays revealed that activity but not the abundance of protein phosphatase-2A was increased by sustained depolarization. Decreased CaMKII activity was accompanied by a selective decrease in dopamine transporter (DAT) mRNA, while tyrosine hydroxylase and actin mRNA abundance was unaltered. On the other hand, brain-derived neurotrophic factor (BDNF) mRNA abundance was increased by sustained depolarization, further demonstrating the specificity of changes. Depolarization also caused a significant decrease in DAT protein abundance and DAT-mediated uptake. Taken together, these data illustrate a novel signaling paradigm in which the activity of protein phosphatase-2A is associated with CaMKII activity and gene expression.