These are a group of four or five proteins embedded in the cell membrane forming a pore. When the drug binds to the receptor, it causes a change in shape of one or more of the proteins which opens the pore and allows ions (usually sodium, potassium or calcium) through. The pore usually opens in a fraction of a millisecond and closes after several milliseconds, so this type of receptor is used for fast neurotransmission. An example is the nicotinic acetylcholine receptor; several clinically important drugs act at these receptors in the neuromuscular junction.
