Electrophysiologic Characteristics of Heteromeric Recombinant NMDA Receptors
The N-methyl-D-aspartate (NMDA) receptor-channel complex is activated by the major excitatory neurotransmitter occurring in central synapses, glutamate. This ligand-gated ion channel displays several unique biophysical and ionic properties originally described in native systems. Particularly noteworthy of these properties are a high permeability to Ca++, a voltage-dependent block by Mg++, slow channel kinetics, and various single-channel conductance states. With the discovery and expression of NR1 and NR2 sub-unit gene products, there has been extensive analysis of these properties in NMDA channels expressed in both Xenopus oocytes and mammalian expression systems. The purpose of this chapter, therefore, is to compare the available data describing channel behavior in native systems with that obtained from expressed receptors. This chapter is divided along the primary aspects of NMDA channel properties: single channel behavior, ionic (Ca++ and Mg++) characteristics and related results of mutational studies in recombinant receptors, and finally, macroscopic kinetic properties.
KeywordsPermeability Magnesium Glycine Glutamine NMDA
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