Reduction of voltage-operated sodium currents by the anticonvulsant drug sulthiame.

The effect of the sulfonamide derivative sulthiame (Ospolot) on voltage-operated sodium channels was investigated in acutely isolated neurons from the guinea pig hippocampus using the whole-cell patch-clamp technique. Sulthiame in a concentration of 10 microg/ml reduced the inactivating sodium currents without affecting potassium currents. The effect was not dependent on voltage. At therapeutic concentration of 1 to 10 microg/ml sodium currents were reduced by 13 to 25% of control. Reductions of this size (induced by the specific sodium channel blocker tetrodotoxin or by 10 microg/ml sulthiame itself) impaired repetitive generation of action potentials and reduced the maximum discharge frequency by 20 to 40%. In summary, the anticonvulsant drug sulthiame exerts blocking effects on sodium channels which can be assumed to be anticonvulsant and to be different from the effects induced by blockade of carbonic anhydrase.