Donepezil (E2020) is a novel cholinesterase inhibitor for the treatment of Alzheimer's disease. Recent studies show that it may act on targets other than acetylcholinesterase in the brain. In the present study, the actions of donepezil on voltage-gated Na+ and K+ channels were investigated in rat dissociated hippocampal neurons. Donepezil reversibly inhibited voltage-activated Na+ current (I(Na)), delayed rectifier K+ current (I(K)) and fast transient K+ current (I(A)). The inhibition of donepezil on I(Na) was dependent on the holding potential. When neurons were held at -100, -80 and -60 mV, the IC50 value was 436+/-19, 291+/-26 and 3.8+/-0.3 microM, respectively. The drug did not affect the activation, fast inactivation of I(Na) and its recovery from fast inactivation. The inhibition of donepezil on I(K) (IC50=78+/-5 microM) was voltage-dependent, whereas that on I(A) (IC50=249+/-25 microM) was voltage-independent. Donepezil caused a significant hyperpolarizing shift of the voltage-dependence of the activation and steady-state inactivation of I(K), without affecting the kinetic properties of I(A). Due to the high concentrations used, the blocking effects of donepezil on the voltage-gated ion channels are unlikely to contribute to the clinical benefits in patients with Alzheimer's disease.