Transient outward potassium current (I_A), highly expressing in hippocampal dendrites, has characteristics of rapid activation and inactivation following appropriate voltage depolarization. I_A is the predominant outward potassium current at the subthreshold range of the action potential and during early phase of repolarization. IA current plays an important role in modulating synaptic input and affecting action potential back-propagation by reducing the speed of depolarization and delaying the action-potential initiation, suggesting its important roles in regulating the electric signal integration and synaptic plasticity. I_A currents have been associated with many diseases, such as seizure.