NCBI Bookshelf. A service of the National Library of Medicine, National Institutes of Health.

Purves D, Augustine GJ, Fitzpatrick D, et al., editors. Neuroscience. 2nd edition. Sunderland (MA): Sinauer Associates; 2001.

  • By agreement with the publisher, this book is accessible by the search feature, but cannot be browsed.
Cover of Neuroscience

Neuroscience. 2nd edition.

Show details

Two Families of Postsynaptic Receptors

The opening or closing of postsynaptic ion channels is accomplished in different ways by two broad families of receptor proteins. The receptors in one family—called ionotropic receptors—are linked directly to ion channels (the Greek tropos means to move in response to a stimulus). These receptors contain two functional domains: an extracellular site that binds neurotransmitters, and a membrane-spanning domain that forms an ion channel (Figure 7.9A). Thus ionotropic receptors combine transmitter-binding and channel functions into a single molecular entity (they are also called ligand-gated ion channels to reflect this concatenation). Such receptors are multimers made up of at least four or five individual protein subunits, each of which contributes to the pore of the ion channel.

Figure 7.9. A neurotransmitter can affect the activity of a postsynaptic cell via two different types of receptor proteins: ionitropic or ligand-gated ion channels, and metabotropic receptors.

Figure 7.9

A neurotransmitter can affect the activity of a postsynaptic cell via two different types of receptor proteins: ionitropic or ligand-gated ion channels, and metabotropic receptors. (A) Ligand-gated ion channels combine receptor and channel functions in (more...)

The second family of neurotransmitter receptors are the metabotropic receptors, so called because the eventual movement of ions through a channel depends on one or more metabolic steps. These receptors do not have ion channels as part of their structure; instead, they affect channels by the activation of intermediate molecules called G-proteins (Figure 7.9B). For this reason, metabotropic receptors are also called G-protein-coupled receptors. Metabotropic receptors are monomeric proteins with an extracellular domain that contains a neurotransmitter binding site and an intracellular domain that binds to G-proteins. Neurotransmitter binding to metabotropic receptors activates G-proteins, which then dissociate from the receptor and interact directly with ion channels or bind to other effector proteins, such as enzymes, that make intracellular messengers that open or close ion channels. Thus, G-proteins can be thought of as transducers that couple neurotransmitter binding to the regulation of postsynaptic ion channels. The postsynaptic signaling events initiated by metabotropic receptors are taken up in detail in Chapter 8.

These two families of postsynaptic receptors give rise to PSPs with very different time courses, producing postsynaptic actions that range from less than a millisecond to minutes, hours, or even days. Ligand-gated ion channel receptors generally mediate rapid postsynaptic effects. Examples are the EPP produced at neuromuscular synapses by ACh (see Figures 7.2 and 7.3), EPSPs produced at certain glutamatergic synapses (see Figure 7.6A), and IPSPs produced at certain GABAergic synapses (see Figure 7.6B). In all three cases, the PSPs arise within a millisecond or two of an action potential invading the presynaptic terminal and last for only a few tens of milliseconds or less. In contrast, the activation of metabotropic receptors typically produces much slower responses, ranging from hundreds of milliseconds to minutes or even longer. The comparative slowness of metabotropic receptor actions reflects the fact that multiple proteins need to bind to each other sequentially in order to produce the final physiological response. Importantly, a given transmitter may activate both metabotropic receptors and ligand-gated ion channels to produce both fast and slow PSPs at the same synapse.

Perhaps the most important principle to keep in mind is that the response elicited by a given neurotransmitter is determined by the postsynaptic complement of receptors and their associated channels. Exactly how postsynaptic responses are produced by some especially important examples of neurotransmitter receptors is considered in the following sections.

Image ch7f2
Image ch7f3
Image ch7f6

By agreement with the publisher, this book is accessible by the search feature, but cannot be browsed.

Copyright © 2001, Sinauer Associates, Inc.
Bookshelf ID: NBK10855

Views

  • Cite this Page
  • Disable Glossary Links

Recent Activity

Your browsing activity is empty.

Activity recording is turned off.

Turn recording back on

See more...