AMPA Receptor Heterogeneity in Rat Hippocampal Neurons Revealed by
Differential Sensitivity to Cyclothiazide.
FLECK, MARK W., ROBERT BˇHRING, DORIS K. PATNEAU?, AND MARK L. MAYER.
Laboratory of Cellular and Molecular Neurophysiology, NICHD, NIH, Building
49 Room 5A78, 49 Convent Drive MSC 4495, Bethesda, MD 20892-4495; and
Department of Pharmacological and Physiological Sciences, University of
Chicago, Chicago, IL 60637.
APStracts 2:0010N, 1996.
SUMMARY AND CONCLUSIONS
1. The kinetics of onset of AMPA receptor desensitization by glutamate, and
the extent of attenuation of AMPA receptor desensitization by cyclothiazide,
showed pronounced cell to cell variation in cultures of rat hippocampal
neurons. Cultures prepared from area CA1 stratum radiatum tended to show
weaker modulation by cyclothiazide than cultures prepared from the whole
hippocampus. 2. Kinetic analysis of concentration jump responses to glutamate
revealed multiple populations of receptors with fast (tf ? 400 ms),
intermediate (ti ? 2-4 s), and slow (ts > 20 s) time constants for recovery
from modulation by cyclothiazide. The amplitudes of these components varied
widely between cells suggesting the existence of at least three populations of
AMPA receptor subtypes, the relative density of which varied from cell to
cell. 3. The complex patterns of sensitivity to cyclothiazide seen in
hippocampal neurons could be reconstituted by assembly of recombinant AMPA
receptor subunits generated from cDNAs encoding the flip (i) and flop (o)
splice variants of the GluR-A and GluR-B subunits. Recovery from modulation by
cyclothiazide was slower for GluR-AiBi and GluR-AoBi than for GluR-AiBo and
GluR-AoBo. 4. Coexpression of the flip and flop splice variants of GluR-A, in
the absence of GluR-B, revealed that heteromeric AMPA receptors with
intermediate sensitivity to cyclothiazide, similar to responses observed for
the combinations GluR-AoBi or GluR-AiBo, could be generated independent of the
presence of the GluR-B subunit. However, recovery from modulation by
cyclothiazide was 2-fold slower for GluR-AiBi than for homomeric GluR-Ai,
indicating that the GluR-A and GluR-B subunits are not functionally equivalent
in controlling sensitivity to cyclothiazide. 5. These results demonstrate that
AMPA receptors expressed in hippocampal neurons are assembled in a variety of
subunit and splice-variant combinations which might serve as a mechanism to
fine-tune the kinetics of synaptic transmission.
Received 20 October 1995; accepted in final form 21 December 1995.
APS Manuscript Number J704-5.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 22 January 96