Metabotropic receptors: their characteristics and functions

Today, a large part of the population knows that brain information is transmitted from bioelectrical impulses that travel to through bundles of neurons or nerves to their destination, allowing this fact both the perception and the action of the internal environment and external.

Said transmission depends on the different neurons being able to establish a connection and transmit either voltage or neurotransmitters, requiring some type of mechanism that allows these elements to be detected and integrated in the postsynaptic neuron to in turn generate or not a reaction in the form of an action potential (or other types of potential). These elements are called receptors. There are mainly two major types of receptors, and metabotropic receptors are one of the most important and well-known.

• Related article: "Types of neurotransmitters: functions and classification"

Basic definition: what is a receiver?

The term receiver is often used in a large number of contexts and fields, being physics, electronics or the judicial field some of them. Another of these contexts is neuroscience, this being the one we focus on in this article.

At the neuron level, we call receptors the set of proteins that are part of the neuronal membrane (or glial, since it has been shown that they also have some receptors) and that They act as a means of communication with the outside of the cell.

These are elements that act as a bridge or lock between the interior and exterior of the neuron, and that it is activated only before the arrival of certain substances (if they are controlled by neurotransmitters) or before certain electrical charges in such a way that open channels through which ions pass that will allow the generation of potentials of different guys. They are especially important in the generation of excitatory and inhibitory potentials, which facilitate or inhibit the possibility of a action potential, and that ultimately allow neural communication and the transmission of information.

There are different types of neurochemical receptors, the two main types being ionotropic and metabotropic receptors. It is the latter that we are going to focus on in this article.

metabotropic receptors

Metabotropic receptors are among the major and most relevant neurochemical receptor types, being activated upon reception with a specific ligand or neurotransmitter. These are receptors that act relatively slowly, since their activation does not generate an immediate opening of the channel but instead triggers a series of processes that end up leading to she.

In the first place, it will be necessary for the neurotransmitter in question to bind to the receptor, something that will generate the activation of the so-called G protein, an element that can either open the channel so that certain ions can enter and/or exit or activate other elements, which will be known as seconds messengers. Thus, the action of these receptors is rather indirect.

Despite the fact that metabotropic receptors are relatively slower than other types of receptor, the truth is that their action is also more durable over time. Another advantage of these receivers is that allow the opening of several channels at the same time, since the second messengers can act in cascade (generating the activation of different proteins and substances) in such a way that the action of the receptors metabotropics can be more multitudinous and more easily allow the generation of some type of potential.

And they not only make it possible to open channels: second messengers can have different actions within of the neuron, being able to even interact with the nucleus without having to open a channel to it.

• You may be interested in: "Types of neurons: characteristics and functions"

Some neurotransmitters with metabotropic receptors

metabotropic receptors are very common in our nervous system, interacting with different types of neurotransmitters. Below we are going to mention some more specific examples of neurotransmitters that serve as ligands to some of the metabotropic type receptors present in our body.

1. Acetylcholine and muscarinic receptors

Acetylcholine is one of the substances that possesses a specific type of metabotropic receptors, the so-called muscarinic receptors. This type of receptor can be both excitatory and inhibitory, generating different effects depending on its location and function.

It is the predominant type of cholinergic receptor in the central nervous system., as well as in the parasympathetic branch of the autonomic nervous system (linked to the heart, intestines and salivary glands).

However, it must be taken into account that acetylcholine also has other types of receptors, nicotinic receptors, which are not metabotropic but ionotropic.

• Related article: "Parts of the Nervous System: functions and anatomical structures"

2. dopamine

Dopamine is another of the substances with metabotropic receptors. In fact, in this case we find that all dopamine receptors are metabotropicThere are different types depending on whether their action is excitatory or inhibitory and whether they act at the pre or postsynaptic level.

3. norepinephrine and adrenaline

As with dopamine, from which it is derived, norepinephrine also has all of its metabotropic-type channels. Adrenaline, derived from norepinephrine, too. They are found both inside and outside the nervous system (for example in adipose tissue) and there are different types depending on whether they are excitatory or inhibitory or if they act pre or postsynaptically.

4. serotonin

Serotonin also has metabotropic receptors, this being the majority type. However, the 5-HT3 receptor is ionotropic. They are mostly inhibitory.

5. Glutamate and the metabotropic receptor

glutamate is one of the main excitatory substances in the brain, but most of its receptors (and the best known, such as NMDA and AMPA) are ionotropic. Only one type of glutamatergic receptor has been identified that is not, receiving the name of metabotropic glutamate receptor.

6. Gamma-aminobutyric acid or GABA

Unlike glutamate, GABA It is the main brain inhibitor. From it, two basic types of receptor have been identified, the GABAb being of the metabotropic type.

Bibliographic references:

• Gomez, M.; Espejo-Saavedra, J.M. and Taravillo, B. (2012). Psychobiology. CEDE PIR Preparation Manual, 12. CEDE: Madrid.
• Kandel, E.R.; Schwartz, J.H.; Jessell, T.M. (2001). Principles of Neuroscience. Madrid: McGrawHill.