Kainate Receptors: What They Are And What Their Functions Are
Kainate receptors They are receptors found in neurons that are activated by the presence of glutamate.
They are not well known and research, to this day, continues trying to elucidate what implication it has in various disorders, especially in epilepsy and diseases such as Alzheimer’s and Parkinson’s. Next we will see what is known about these peculiar ionotropic receptors.
Kainate receptors They are found in the neuronal membrane and respond to the presence of glutamate Traditionally they were classified as non-NMDA receptors, along with the AMPA receptor.
Kainate receptors are less understood by the scientific community compared to AMPA and NMDA, which are also ionotropic receptors for the neurotransmitter glutamate.
Glutamate is known to act as the primary agent at most excitatory synapses of the central nervous system (CNS). It is a substance that mediates synaptic transmission and, when the nervous system is being formed, it participates in the processes of neuronal growth and maturation, in addition to being involved in the formation and elimination of synapses, and being involved in the processes of learning and memory formation.
The receptors activated by this neurotransmitter have been divided into two families: metabotropic and ionotropic:
Metabotropics are coupled to G proteins and regulate the production of intracellular messengers
Ionotropics, where kainate receptors would be found, they form a cation channel with different selectivity for certain ions being permeable to several ions: sodium (Na+), potassium (K+) and calcium (Ca+2).
Among the ionotropic glutamate receptors are, as we have already mentioned, kainate receptors, NMDA (N-methyl-D-aspartic acid) receptors and AMPA (a-amino-3-hydroxy-5-methyl-acid) receptors. 4-isoxazolepropionic acid).
Postsynaptic kainate receptors are involved in excitatory neurotransmission, while presynaptic receptors are involved in inhibitory neurotransmission, modulating GABA release through a presynaptic mechanism.
Structure
Up to five types of kainate receptor subunits are known: GluR5 (GRIK1), GluR6 (GRIK2), GluR7 (GRIK3), KA1 (GRIK4) and KA2 (GRIK5), which are similar to the subunits of AMPA and NMDA receptors.
GluR subunits 5 to 7 can form homomeric channels , that is, making the receptor exclusively composed of one type of those subunits; or heteromers, meaning that there can be more than one type of subunit. The KA1 and KA2 subunits can only form functional receptors by combining with GluR subunits 5 to 7.
Molecularly speaking, ionotropic glutamate receptors They are integral membrane proteins, formed by four subunits organized in a tetramer
Distribution
Kainate receptors are distributed throughout the nervous system, although their expression patterns of the subunits that make them up differ depending on the region:
1. GluR5 subunit
The GluR5 subunit is found, above all, in neurons of the dorsal root ganglia, septal nucleus, piriform and cingulate cortex, subiculum, and Purkinje cells cerebellar.
2. GluR6 subunit
GluR6 is widely found in granule cells of the cerebellum, dentate gyrus, and CA3 region of the hippocampus in addition to the striatum.
3. GluR7 subunit
The GluR7 subunit is sparsely found in the brain, but is expressed, especially strongly, in the deep cerebral cortex and striatum, as well as in inhibitory neurons of the molecular layer of the cerebellum.
The KA1 subunit is located in the CA3 region of the hippocampus and has also been found in the amygdala, entorhinal cortex, and dentate gyrus. KA2 is found in all nuclei of the nervous system
Conductance
The ion channel formed thanks to kainate receptors is permeable to sodium and potassium ions. Its conductance is similar to that of AMPA receptor channels, about 20 pS (petasiemens).
However, kainate receptors differ from AMPA receptors in that the postsynaptic potentials generated by kainate receptors are slower than the postsynaptic potentials of AMPA receptors.
Synaptic function
As we were previously commenting, kainate receptors They are involved in both presynaptic and postsynaptic action They are found in smaller quantities in the brain than AMPA and NMDA receptors.
The most recent research has discovered that these types of receptors not only have an ionotropic function, directly changing the conductivity of the neuronal membrane, but also, may involve changes at the metabotropic level, affecting protein production
It should be said that kainate is an excitotoxic substance, and causes seizures and neuronal damage, phenomena very similar to those seen in the neurons of people who suffer from epilepsy. That is why, and taking into account that all this is closely related to glutamate neurotransmission problems, research has linked problems in kainate receptors with various psychological disorders, medical problems and neurodegenerative diseases.
To date, problems in the synaptic function of kainate receptors have been linked to ischemia, hypoglycemia, epilepsy, Alzheimer’s disease, Parkinson’s disease, schizophrenia bipolar disorder, autism spectrum disorders, Huntington’s chorea, and amyotrophic lateral sclerosis (ALS). Most studies have found these relationships with mutations in GluK subunits 1 through 5.
Kainate receptors take a rather modest role in synapses compared to AMPA receptors. They have a very subtle role in synaptic plasticity, affecting the probability that the postsynaptic cell will send a response to a future stimulus.
Activation of kainate receptors in the presynaptic cell can affect the amount of neurotransmitters to be released into the synaptic space. This effect can occur quickly and have effects for a long time, and repeated stimulation of kainate receptors can lead to addiction over time.
