Effects of valproate on early and late potassium currents of single neurons.

The effects of valproate sodium (VPA) on potassium currents were tested in identified neurons of the snail Helix pomatia. VPA was extracellularly and intracellularly applied. VPA (i) had no effects on the current-voltage relation of the early potassium outward current (IA), (ii) shifted the steady state inactivation function of IA to more positive potentials, (iii) increased the amplitude of the late potassium outward currents. It is suggested that the extrasynaptic effects on potassium currents markedly contribute to the antiepileptic and antimanic effects of VPA.