Voltage Gated Sodium (Na+) Channel

Channels in the outer membranes of bacteria, mitochondria, and chloroplasts have relatively large and permissive pores, and it would be disastrous if they directly connected the interior of a cell to an extracellular space. In fact, many bacterial toxins do exactly that to kill other cells. In contrast, most of the channels in the plasma membrane of animal and plant cells that connect the cytosol to the outside of the cell necessarily have narrow and highly selective pores that can open and close rapidly. Because these proteins are specifically related to inorganic ion transport, they are known as ion channels. For transport efficiency, ion channels have an advantage over transporters, they can pass up to 100 million ions through an open channel every second, a rate 105 times higher than the fastest transport rate mediated by any known transporter. Channels cannot be coupled to an energy source to perform active transport, so the transport they mediate is always passive (downhill). Therefore, the function of ion channels is to allow specific inorganic ions - mainly Na +, K +, Ca2 + or Cl - to diffuse rapidly through their electrochemical gradients through the lipid bilayer.