Metabotropic Receptors: Their Characteristics And Functions
Nowadays, a large part of the population knows that brain information is transmitted from bioelectric impulses that travel through bundles of neurons or nerves to their destination, allowing both the perception and the action of the internal and external environment. .
This 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 into the postsynaptic neuron to in turn generate or not a reaction in form of action potential (or other types of potential). These elements are called receptors. There are mainly two main types of receivers, and metabotropic receptors are one of the most important and well-known
The term receiver is often used in a large number of contexts and areas, some of them being physics, electronics or the judicial field. 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 inside and outside of the neuron, and that It is activated only upon the arrival of certain substances (if they are controlled by neurotransmitters) or when faced with certain electrical charges in such a way that they open channels through which ions pass that will allow the generation of potentials of different types. They are especially important in the generation of excitatory and inhibitory potentials, which facilitate or inhibit the possibility of an action potential appearing, and which ultimately allow neuronal 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 main and most relevant types of neurochemical receptors, activated from 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 it.
First of all, it will be necessary for the neurotransmitter in question to bind to the receptor, something that will generate the activation of what is known as the G protein, an element that can either open the channel so that certain ions can enter and/or leave or activate other elements. , who will be known as second messengers. Thus, the action of these receptors is rather indirect.
Although metabotropic receptors are relatively slower than other types of receptor, the truth is that their action is also longer lasting 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 metabotropic receptors 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 the neuron, and can even interact with the nucleus without having to have opened a channel to do so.
Some neurotransmitters with metabotropic receptors
Metabotropic receptors They are very common in our nervous system, interacting with different types of neurotransmitters. Below we are going to mention some more specific examples of the neurotransmitters that serve as ligands for some of the metabotropic receptors present in our body.
1. Acetylcholine and muscarinic receptors
Acetylcholine is one of the substances that has 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.
2. Dopamine
Dopamine is another substance with metabotropic receptors. In fact, in this case we find that all dopamine receptors are metabotropic there are different types depending on whether their action is excitatory or inhibitory and whether they act at a pre- or postsynaptic level.
3. Norepinephrine and adrenaline
As with dopamine, from which it is derived, norepinephrine also has all its metabotropic 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 whether they act pre- or postsynaptically
4. Serotonin
Serotonin also has metabotropic receptors, this being the majority type. However, the 5-HT3 receptor is ionotropic. Most of them are of the inhibitory type.
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 glutamatergic, simply receiving the name metabotropic glutamate receptor.
6. Gamma-aminobutyric acid or GABA
Unlike glutamate, GABA is the main brain inhibitor. Two types of basic receptors have been identified, GABAb being metabotropic.
