Valproic acid selectively reduces the low-threshold (T) calcium current in rat nodose neurons

Valproic acid (VPA) is an antiepileptic drug used in the treatment of a wide variety of human seizures including generalized absence (GA) (petit mal) seizures. The mechanism of action of VPA in controlling GA seizures is not known. We tested the effects of VPA on the Ca2+ current components of acutely dissociated rat nodose ganglion neurons. VPA reduced the low-threshold (T) Ca2+ current at clinically relevant concentrations but had no effect on the high-threshold (N and L) current components. The effect on T current was concentration-dependent and most apparent at peak current. There was little effect seen on late current. VPA did not affect the rate or voltage-dependency of T current activation. The selective reduction of T current may be a means by which VPA is effective in controlling GA seizures.