Poulsen, Mette Homann3; Lucas, Simon4; Strømgaard, Kristian3; Kristensen, Anders Skov3
1 Medicinal Chemistry Research, Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, Københavns Universitet2 Department of Drug Design and Pharmacology, Faculty of Pharmaceutical Sciences, Københavns Universitet3 Medicinal Chemistry Research, Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, Københavns Universitet4 Department of Drug Design and Pharmacology, Faculty of Pharmaceutical Sciences, Københavns Universitet
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 IC50 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 IC50 values in the nanomolar range (252-356 nM), and heteromeric GluA1/A2 and GluA2/A3 receptors nonselectively, with IC50 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.
Molecular Pharmacology, 2014, Vol 85, Issue 2, p. 261-268