A metabotropic receptor, also referred to by the broader term G-protein-coupled receptor, is a type of membrane receptor that initiates a number of metabolic steps to modulate cell activity. The

nervous system In biology, the nervous system is the complex system, highly complex part of an animal that coordinates its behavior, actions and sense, sensory information by transmitting action potential, signals to and from different parts of its body. Th ...

utilizes two types of receptors: metabotropic and ionotropic receptors. While ionotropic receptors form an ion channel pore, metabotropic receptors are indirectly linked with ion channels through signal transduction mechanisms, such as

G protein G proteins, also known as guanine nucleotide-binding proteins, are a Protein family, family of proteins that act as molecular switches inside cells, and are involved in transmitting signals from a variety of stimuli outside a cell (biology), ...

s. These two types of receptors, along with their number and activity level, form the basis of the sympathetic and parasympathetic nervous systems and play key roles in regulating rates of resting energy expenditure (REE), resting heart rate, heart rate variability, and global myocardial oxygen consumption. Both receptor types are activated by specific chemical ligands. 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 can also result in ion channels opening or other intracellular events, but involve a range of second messenger chemicals.

Mechanism

Chemical messengers bind to metabotropic receptors to initiate a diversity of effects caused by biochemical signaling cascades. G protein-coupled receptors are all metabotropic receptors. When a ligand binds to a G protein-coupled receptor, a guanine nucleotide-binding protein, or

, activates a second messenger cascade which can alter gene transcription, regulate other proteins in the cell, release intracellular Ca²⁺, or directly affect ion channels on the membrane. These receptors can remain open from seconds to minutes and are associated with long-lasting effects, such as modifying synaptic strength and modulating short- and long-term synaptic plasticity. Metabotropic receptors have a diversity of ligands, including but not limited to: small molecule transmitters, monoamines,

peptides Peptides are short chains of amino acids linked by peptide bonds. A polypeptide is a longer, continuous, unbranched peptide chain. Polypeptides that have a molecular mass of 10,000 Dalton (unit), Da or more are called proteins. Chains of fewer t ...

hormone A hormone (from the Ancient Greek, Greek participle , "setting in motion") is a class of cell signaling, signaling molecules in multicellular organisms that are sent to distant organs or tissues by complex biological processes to regulate physio ...

s, and even gases. In comparison to fast-acting

neurotransmitter A neurotransmitter is a signaling molecule secreted by a neuron to affect another cell across a Chemical synapse, synapse. The cell receiving the signal, or target cell, may be another neuron, but could also be a gland or muscle cell. Neurotra ...

s, these ligands are not taken up again or degraded quickly. They can also enter the

circulatory system In vertebrates, the circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the body. It includes the cardiovascular system, or vascular system, that consists of the heart ...

to globalize a signal. Most metabotropic ligands have unique receptors. Some examples include: metabotropic glutamate receptors, muscarinic acetylcholine receptors, GABA_B receptors.

Structure

The G protein-coupled receptors have seven hydrophobic transmembrane domains. Most of them are monomeric proteins, although GABA_B receptors require heterodimerization to function properly. The protein's

N terminus N, or n, is the fourteenth letter of the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages, and others worldwide. Its name in English is ''en'' (pronounced ), plural ''ens''. History ...

is located on the extracellular side of the membrane and its C terminus is on the intracellular side. The 7 transmembrane spanning domains, with an external amino terminus, are often claimed as being alpha helix shaped, and the polypeptide chain is said to be composed of around 450–550 amino acids.

Mechanism

Structure

References

Further reading