Enhanced functional detection of synaptic calcium-permeable AMPA receptors using intracellular NASPM

• Published in: eLife Vol. 12
• Main Authors: Coombs, Ian, Bats, Cécile, Sexton, Craig A, Studniarczyk, Dorota, Cull-Candy, Stuart G, Farrant, Mark
• Format: Journal Article
• Language: English
• Published: England eLife Sciences Publications Ltd 12.04.2023; eLife Sciences Publications, Ltd
• Subjects: AMPA-type glutamate receptor; Animals; Calcium (intracellular); Calcium - metabolism; Calcium permeability; Calcium, Dietary; excitatory postsynaptic current; Glutamic acid receptors; Intracellular; Ions; Membrane Proteins - metabolism; Mice; NASPM; Neuronal-glial interactions; Neurons - physiology; Neuroscience; Polyamines; Receptors, AMPA - metabolism; rectification; Regulatory proteins; Spermine; Spermine - metabolism; Spermine - pharmacology; Synaptic plasticity; TARP; Tools and Resources; Toxins; α-Amino-3-hydroxy-5-methyl-4-isoxazole propionic acid; α-Amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptors; mouse; AMPA-type glutamate receptor; NASPM; neuroscience; rectification; spermine; TARP; excitatory postsynaptic current
• ISSN: 2050-084X; 2050-084X
• DOI: 10.7554/eLife.66765

Calcium-permeable AMPA-type glutamate receptors (CP-AMPARs) contribute to many forms of synaptic plasticity and pathology. They can be distinguished from GluA2-containing calcium-impermeable AMPARs by the inward rectification of their currents, which reflects voltage-dependent channel block by intracellular spermine. However, the efficacy of this weakly permeant blocker is differentially altered by the presence of AMPAR auxiliary subunits - including transmembrane AMPAR regulatory proteins, cornichons, and GSG1L - which are widely expressed in neurons and glia. This complicates the interpretation of rectification as a measure of CP-AMPAR expression. Here, we show that the inclusion of the spider toxin analog 1-naphthylacetyl spermine (NASPM) in the intracellular solution results in a complete block of GluA1-mediated outward currents irrespective of the type of associated auxiliary subunit. In neurons from GluA2-knockout mice expressing only CP-AMPARs, intracellular NASPM, unlike spermine, completely blocks outward synaptic currents. Thus, our results identify a functional measure of CP-AMPARs, that is unaffected by their auxiliary subunit content.