Autophosphorylation Versus Dephosphorylation of Ca²⁺/Calmodulin-Dependent Protein Kinase II

Abstract

The hypothesis that usage-dependent change in the transmission efficiency of a synapse is a cellular representation of memory formation in the brain has been a foundation of modern neuroscience. Long-term potentiation (LTP) has been studied, most extensively in rat hippocampus, as an experimental model for this hypothesis. Considerable efforts have been made for elucidation of molecular mechanisms of LTP. Although Molecular-signal transductions responsible for LTP might be very complicated and the entire picture of them has not yet been established, evidence has been accumulating strongly suggesting that Ca^,+/calmodulin-dependent protein kinase II (CaMKII) plays a crucial role in LTP [1]: CaMKII is highly concentrated in the postsynaptic region, which makes this enzyme a good target of Ca²⁺ influx through NMDA-receptor/channels known to be necessary for the induction of LTP; specific inhibitors of CaMKII prevent LTP; postsynaptic injection of a constitutively active form of CaMKII results in LTP-like enhancement of synaptic transmission [2]; and mice lacking aCaMKII gene are deficient in LTP. Therefore, tracing CaMKII activity in LTP will be incisive for understanding the main stream of molecular-signal transductions responsible for LTP. In the present study, we addressed this issue by theoretical investigation of an integrated model for postsynaptic biochemical-reaction networks involving CaMKII. Each plot of the networks was modelled on the basis of reports from in vitro experimental studies done for purified enzymes.