Surface Receptors Linked Directly to Ion Channels

Membrane receptors may be involved directly in the cellular response to the drug by acting as an ion pore and thus changing the membrane permeability.61 

Perhaps the most well-known example is the acetylcholine receptor located on the postsynaptic membrane of the neuromuscular junction49 56 (Fig. 4-1). When bound by acetylcholine molecules, the receptor activates and opens a pore through the cell membrane, thereby increasing the permeability of the muscle cell to sodium.38 56 This action results in depolarization and excitation of the cell because of sodium influx. Another important example of a receptor-ion channel system is the gamma-aminobutyric acid (GABA)-benzodiazepine-chloride ion channel complex found on neuronal membranes in the central nervous sys- 

FIGURE 4-1 Schematic model of the acetylcholine receptor, an example of a surface receptor that is linked directly to an ion channel. Binding of two acetylcholine (ACh) molecules to the outer surface of the receptor protein induces the opening of a central ion channel, thus allowing sodium to enter the cell. 

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