Some science behind the scenes
Channel blockers - sodium
A sodium channel is just one that allows sodium ions to go through or as the text books say “displays selective permeability to sodium ions”. They conduct [via the channel] sodium ions (Na+) through a cell's plasma membrane, so that the nerve can work. They are classified according to the trigger that opens the channel for such ions, which can be a voltage-change - ‘voltage-gated sodium channels’ - or binding of a substance (a ligand) to the channel – ‘ligand-gated sodium channels’.
Sodium channel blockers block or impair the conduction of sodium ions (Na+) through sodium channels. Many toxins work by blocking the sodium channels, for example tetrodotoxin and saxitoxin work by blocking the extracellular pore opening of the channel.
Conversely the pharmaceuticals tend to block from the intracellular side of the channel. There are three types of pharmaceutical that work this way
- Local anaesthetics
- Antiarrhythmic agents [called class I agents]
- Some anticonvulsants