Kinetically distinguishable AMPA receptors in rat hippocampus are associated with the loss of glutamate-sensitive conformational transitions

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Abstract

We describe a stopped-flow method to study α-amino-7-hydroxy-5-methyl-4-isoxazole propionate (AMPA)-kainate receptor-mediated Na+ ion flux through native membranes. Resealed plasmalemma vesicles and nerve endings from the rat hippocampus were mixed rapidly with a membrane impermeant form of the fluorescence indicator, sodium binding benzofurane oxazole and the changes in fluorescence intensity in response to various [Glu] on the time scale of 0.04 ms-10 s were monitored at a sampling rate of 6.55 kHz. Inhibitors like ouabain (1 mM) and 5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate (dizocilpine, 50 μM) enhanced Na+ ion translocation under low-[Na+] and physiological conditions, respectively. Dependence of AMPA-kainate receptor kinetics on [Glu] was described in a model of channel activation by faster and slower desensitizing receptors. The model accounted for almost all of the Na+ ion flux activity in the 30 μM-10 mM range of [Glu]. We found that the values of the initial rate constant for Na+ ion influx, J(A), and rate constant for desensitization, α, for the faster desensitizing receptor were dependent on data sampling rate, whereas the initial rate constant for Na+ ion flux through the slower desensitizing receptor, J(B), varied much less with the sampling rate. These phenomena can be described by (1) a fractal model of short-lived AMPA-kainate receptor channel with many closely spaced states (fractal dimension ~1.8) and (2) a model of long-lived AMPA-kainate receptor channel with two discrete states. Copyright (C) 1999 Elsevier Science Ltd.

Original languageEnglish
Pages (from-to)83-90
Number of pages8
JournalNeurochemistry international
Volume36
Issue number1
DOIs
Publication statusPublished - Jan 1 2000

Keywords

  • Dizocilpine
  • Fractal kinetics
  • Hippocampal AMPA-kainate receptors
  • Ouabain
  • Stopped-flow method
  • Transmembrane NA ion flux

ASJC Scopus subject areas

  • Cellular and Molecular Neuroscience
  • Cell Biology

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