Evaluation of PhTX-74 as subtype-selective inhibitor of GluA2-containing AMPA receptors.
The α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptors (AMPARs) are glutamate-gated cation channels that mediate fast excitatory synaptic transmission in the central nervous system. AMPARs are tetramers formed by homo- or heteromeric assembly of GluA1-4 subunits to produce multiple subtypes with varying biophysical properties. Polyamine toxins such as joro spider toxins, philanthotoxins (PhTXs), and argiotoxins are use-dependent ion channel blockers of AMPARs widely employed as highly potent antagonists of GluA2-lacking receptor subtypes. In addition to this use, recent findings have indicated that a philanthotoxin analog, PhTX-74, can distinguish among GluA2-containing AMPAR subtypes in the presence of the prototypical transmembrane AMPAR regulatory protein γ-2 (or stargazin). Thus, PhTX-74 may be of potential use in studies of the neurobiological role of GluA2-containing subtypes. We have evaluated the pharmacological profile of PhTX-74 and related polyamine toxins at homo- and heteromeric AMPARs in the presence and absence of γ-2. Determination of IC(50) values for inhibition of glutamate-evoked currents from Xenopus oocytes expressing recombinant homo- or heteromeric combinations of GluA1, GluA2, and GluA3 in the presence of γ-2 shows that PhTX-74 inhibits homomeric GluA1 and GluA3 receptors nonselectively, with IC(50) values in the nanomolar range (252-356 nM), and heteromeric GluA1/A2 and GluA2/A3 receptors nonselectively, with IC(50) values in the micromolar range (22 μM). Thus, in contrast to earlier findings, we find that PhTX-74 cannot pharmacologically discriminate between GluA2-containing AMPAR subtypes.
Department of Drug Design and Pharmacology, University of Copenhagen, Denmark.
Mette H
MH
Poulsen
Simon
S
Lucas
Kristian
K
Strømgaard
Anders S
AS
Kristensen
D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D010636:Phenols / Q000494:pharmacology*; D011073:Polyamines / Q000494:pharmacology*; D021122:Protein Subunits; D018091:Receptors, AMPA / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000145:classification / Q000502:physiology; D014981:Xenopus
D010636:Phenols; D011073:Polyamines; D021122:Protein Subunits; D018091:Receptors, AMPA; C520929:philanthotoxin-7,4; D002118:Calcium