Voltage-dependent action of valproate on potassium channels in frog node of Ranvier

The influence of the anti-epileptic drug, valproate, on K conductance (g K) was investigated in voltage-clamped Ranvier nodes of Xenopus laevis. A double pulse method was used in order to eliminate the effect of accumulation of potassium ions in the perinodal space, thus enabling the determination of the ‘true’ magnitude of g K. Valproate (2.4 mM) had a voltage-dependent action on the magnitude of g K. With small step depolarizations more negative than about −50 mV, valproate increased g K (20 ms after the step) to approximately 12% of the maximal g K, an increase which disappeared due to a relatively rapid (