DefinitionThis section has been translated automatically.
AMPA receptors (AMPA-R - acronym for α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor) are ionotropic glutamate receptors. Ionotropic receptors activate membrane channels where ions can pass through when open. They are specialized for rapid excitation. In many synapses, they produce their stimulatory electrical responses in a fraction of a millisecond after stimulation. Excitation of the postsynaptic membrane by glutamate leads to its depolarization by the AMPA receptors. This results in an "excitatory postsynaptic potential" - EPSP-. Only high frequency repetitive depolarization (25-200Hz) or simultaneous depolarization through multiple converging coincident synapses leads to charge repulsion of the Mg ion on the NMDA receptor and its opening. This then leads to calcium influx into the postsynapse and increased intracellular Ca concentration.
PathophysiologyThis section has been translated automatically.
The AMPA receptor is permeable to Na+ , K+ and partially also to Ca2+ ions. In contrast to NMDA receptors, whose main function is rather the modulation of synaptic transmission, AMPA receptors mediate more the fast excitatory synaptic transmission per se. While the number of NMDA receptors in the postsynaptic membrane is largely constant, AMPAeceptors undergo high turnover and are rapidly inserted and removed from the postsynaptic membrane (Contractor A et al. 2002; Malinow R 2002). Thus, the number of postsynaptic AMPAreceptors determines the strength of synaptic transmission (deSouza S 2002).
AMPA receptors have a pentameric structure. Four different subunits have been described, GLUR1-GLUR4. The electrophysiological properties of AMPA receptors are determined by these subunits. A receptor can be either homomeric or heteromeric in composition.
At many excitatory synapses, NMDA receptors are colocalized with AMPA receptors. Presynaptic release of glutamate can thus lead to AMPAreceptor-mediated pre-depolarization of the postsynaptic cell. As a result, the Mg2+ block is released from the ion channel of the NMDA receptor, and NMDA receptor-mediated ionic currents can flow.