TABLE 3. Ionotropic glutamate receptors: AMPA/kainatea

Subunit

Channel assembly

Characteristics

Agonist selectivity

AMPA-preferring

GluR1

Homomeric or heteromeric

RNA splicing generates alternate "flip" or "flop"

AMPA > KA

GluR2

variants

GluR3

GluR4

In heteromeric channels, GluR2 limits Ca2+

permeabilityb

Kainate-preferring

GluR5

Homomeric or heteromeric

Low-affinity KA binding

KA >> AMPA

GluR6

GluR7

Heteromeric only

Low-affinity KA binding

KA >> AMPA

KA1

Heteromeric only

High-affinity KA binding

KA >> AMPA

KA2

a Adapted from ref. 29.

b The low Ca2+ permeability of GluR2 appears to be conferred by RNA editing to change a single residue in the second transmembrane domain from a glutamine to an arginine. Similar RNA editing of this "Q/R site" in GluR5 and GluR6 generates two alternate forms of these subunits with different Ca2+ permeabilities. GluR1-GluR4 are also known as GluRA-GluRD.
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published 2000