Blockages in repolarization can arise due to modifications of the voltage-gated K channels. This is demonstrated with selectively blocking voltage gated K channels with the antagonist tetraethylammonium (TEA). By blocking the channel, repolarization is effectively stopped. Dendrotoxins are another example of a selective pharmacological blocker for voltage gated K channels. The lack of repolarization means that neuron stays at a high voltage, which slows sodium channel deactivation to a point where there is not enough inwards Na current to depolarize and sustain firing.