Voltage-gated sodium and T-type calcium channels

Class

small molecule; sulfonamide anticonvulsant; also a weak carbonic anhydrase inhibitor (contribution to efficacy unknown); does not potentiate GABA or glutamate synaptic responses

Pathway

blocks sodium channels and reduces voltage-dependent, transient inward T-type Ca2+ currents, stabilizing neuronal membranes and suppressing synaptically-driven electrical activity.

Voltage-gated sodium channels and T-type calcium channels are membrane proteins that control the electrical excitability of neurons. Sodium channels open transiently to generate the rapid depolarization phase of the action potential, the electrical signal that lets one neuron fire and propagate a message. T-type calcium channels activate near resting membrane potential and produce brief, low-threshold calcium currents that support rhythmic firing, particularly in thalamic circuits that pace normal and abnormal oscillatory activity. In epilepsy, neurons within a seizure focus fire excessively and synchronously with neighboring circuits, and both channel types contribute to this hyperexcitability. A sulfonamide anticonvulsant that blocks sodium channels and dampens T-type calcium currents can limit sustained high-frequency firing at a seizure focus while also interrupting thalamocortical oscillations underlying certain generalized seizure types. Combining actions on both channel families offers coverage across seizure types with different underlying circuit mechanisms, an advantage over an agent addressing only one. This class acts independently of the synaptic neurotransmitter systems gamma-aminobutyric acid (GABA) and glutamate, distinguishing its mechanism from anticonvulsants that primarily enhance inhibitory or dampen excitatory synaptic transmission. This dual channel-blocking mechanism is broadly relevant to epilepsy and other conditions of neuronal hyperexcitability.