AMPA receptor

AMPA receptors ( AMPAR, eng; . Α -amino -3-hydroxy -5-methyl -4- isoxazolepropionic acid receptor ) form in addition to the NMDA and kainate receptors, a sub-group of glutamate receptors are the most common neurotransmitter receptors in the central nervous system. Forming cation channels that mediate the rapid component of the post-synaptic current. Their activation causes changes in conductivity in the postsynaptic membrane produced for a duration of a few milliseconds. Their name from the AMPA receptors to the synthetic agonist AMPA ( α -amino -3-hydroxy -5-methyl -4 -isoxazole - propionic acid), with which they can be specifically activated.

AMPA receptors are composed of four subunits, each with a mass of about 100 kDa. The sequence similarity between the subunits is about 70%. There are four AMPA receptor subunits which are designated GluR1, GluR2 to 4 ( GluR - A to D ).

The individual subunits consist of about 900 amino acids. The N-termini of the subunits lie extracellular C -termini intracellularly. The polypeptide of subunit crosses the membrane three times, and forming the membrane on the intracellular side a loop. The loops of the four subunits together form the ion channel ( Fig. 1 ).

The GluR subunits come in two forms, the so-called " flip " - and " flop" forms before. They differed by the absence or presence of an alternatively spliced ​​exons. This results in 38 amino acid residues that precede the last transmembrane domain. The flip of the GluR subunits show a slower desensitization of AMPA - receptor as the flop forms.

Ion specificity of the AMPA receptors (i.e., its relative conductivity is sodium, potassium or calcium ions) depends on the combination of the units of which they are composed, from. In contrast to GluR1 GluR2, GluR3 and GluR4 are generally permeable to calcium ions. Usually GluR2 -containing AMPA receptors are not permeable to calcium ions. This is because that the transcript of the GluR2 subunit is modified by the enzyme adenosine deaminase. This change results in the second transmembrane domain to an amino acid change from glutamine to arginine, thereby receptors that the GluR2 subunit contain their conductivity for calcium ions lose.

The GluR2 subunit is also important for the relationship between the membrane potential and current through the AMPA - receptor. The current through receptors without GluR2 is away rektifizierend. This means that only when a negative value of the membrane potential, a current flows through the ion channel, but not in the positive. In the presence of the GluR2 current-voltage relationship of AMPA receptors, however, is linear.

AMPA receptors are important for synaptic plasticity. At many synapses, such as the hippocampus or cerebellum, the density of the AMPA receptor is regulated depending on the activity of the synapse to the post-synaptic membrane.