This MedLibrary.org supplementary page on Metabotropic is provided directly from the open source Wikipedia as a service to our readers. Please see the note below on authorship of this content, as well as the Wikipedia usage guidelines. To search for other content from our encyclopedia supplement, please use the form below:
Related Sponsors
Metabotropic receptor is a subtype of membrane receptors at the surface or in vesicles of eukaryotic cells.
In the nervous system, based on their structural and functional characteristics, neurotransmitter receptors can be classified into two broad categories: metabotropic and ionotropic receptors. In contrast to the latter, metabotropic receptors do not form an ion channel pore; rather, they are indirectly linked with ion-channels on the plasma membrane of the cell through signal transduction mechanisms.
What both receptor types have in common is that they are activated by specific neurotransmitters. When an ionotropic receptor is activated, it opens a channel that allows ions such as Na+, K+, or Cl- to flow. In contrast, when a metabotropic receptor is activated, a series of intracellular events are triggered that also results in ion channel opening but must involve a range of second messenger chemicals.
Contents |
Examples
This class of receptors includes the metabotropic glutamate receptors, muscarinic acetylcholine receptors, GABAB receptors, and most serotonin receptors, as well as receptors for norepinephrine, epinephrine, histamine, dopamine, neuropeptides (Austin, 2004; Purves et al., 2001) and endocannabinoids.
Structure
All metabotropic receptors are monomeric proteins with seven transmembrane domains. The protein's N terminus is on the extracellular side of the membrane and its C terminus is on the intracellular side (Purves et al., 2001).
Function
Metabotropic receptors have neurotransmitters as ligands, which, when bound to the receptors, initiate cascades that can lead to channel-opening or other cellular effects. When a ligand, also called the primary messenger, binds to the receptor, or the transducer, the latter activates a primary effector, which can go on to activate secondary messengers or have other effects. Since opening channels by metabotropic receptors involves activating a number of molecules in turn, channels associated with these receptors take longer to open than ionotropic receptors do, and they are thus not involved in mechanisms that require quick responses (Kandel et al., 2000, p. 240). However, metabotropic receptors also remain open from seconds to minutes (Kandel et al., 2000, p. 250-251). Thus they have a much longer-lasting effect than ionotropic receptors, which open quickly but only remain open for a few milliseconds (Austin, 2004). While ionotropic channels have an effect only in the immediate region of the receptor, the effects of metabotropic receptors can be more widespread through the cell.
Metabotropic receptors can both open and close channels. They can make a membrane more excitable by closing K+ channels, retaining positive charge within the cell and thus reducing the amount of current necessary to cause an action potential (Kandel et al., 2000, p. 242-243). Metabotropic receptors on the presynaptic membrane can inhibit or, more rarely, facilitate neurotransmitter release from the presynaptic neuron (Schmitz et al., 2001). These receptors can be further classified into receptor tyrosine kinases and G protein-coupled receptors, or GPCRs (Kandel et al., 2000, p. 229).
References
- Austin V. 2004. Fundamentals of the nervous system and nervous tissue. Pearson Education, Inc., Benjamin Cummings. From, Marieb E.N. 2004. Human Anatomy & Physiology, Sixth Edition. [1]
- Kandel ER, Schwartz JH, Jessell TM. Principles of Neural Science, 4th ed., pp.178-180. McGraw-Hill, New York (2000). ISBN 0-8385-7701-6
- Purves D., Augustine G.J., Fitzpatrick D., Katz L.C., LaMantia A.S., McNamara J.O., and Williams S.M. 2001. Neuroscience, Second Edition. Sinauer Associates, Inc. [2]
- Schmitz D, Mellor J, Nicoll RA. Presynaptic kainate receptor mediation of frequency facilitation at hippocampal mossy fiber synapses. Science. 9 March 2001;291(5510):1972-6. PMID 11239159
- Zimmerberg, B. 2002. Dopamine receptors: A representative family of metabotropic receptors. Multimedia Neuroscience Education Project. [3]
External links
|
|||||||||||||||||||||||||||||
Wikipedia content modification information:
- This page was last modified on 31 July 2008, at 22:24.
Wikipedia Authorship and Review
Wikipedia content provided here is not reviewed directly by MedLibrary.org. Wikipedia content is authored by an open community of volunteers and is not produced by or in any way affiliated with MedLibrary.org.
Wikipedia Usage Guidelines
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article on "Metabotropic".
The URL for this specific entry is:
All Wikipedia text is available under the terms of the GNU Free Documentation License. (See Copyrights for details). Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc.