Pharmacological differentiation between neuronal and recombinant glutamate receptor channels expressed in Xenopus oocytes

To determine the molecular components of neuronal glutamate receptors, it is important to identify pharmacological tools that allow differentiation between different glutamate receptor types. Here, we utilized the naphthalene derivative Evans Blue (EB) and a collection of other subtype-specific compounds (polyamine toxins, concanavalin A, cyclothiazide) to compare the pharmacological profile of neuronal and recombinant glutamate receptors GluR1-GluR6 expressed in Xenopus oocytes. Submicromolar concentrations of EB selectively reduced the activity of homomeric glutamate receptors GluR1, GluR2(Q) and GluR4. Applied at concentrations above 100 mu M, EB potentiated kainate responses of receptors GluR1, GluR3 and GluR4, while receptors GluR2(Q) and GluR6(Q) were completely blocked. Similar experiments were performed on identified neurones in brain slices and after injection of rat brain RNA in Xenopus oocytes. Neuronal kainate responses were (i) potentiated by 100 mu M cyclothiazide, (ii) slightly blocked after preincubation in 10 mu M concanavalin A, and (iii) not significantly affected by either low (< 1 mu M) or high (> 100 mu M) concentrations of EB. Their pharmacological properties were markedly different from those of recombinant glutamate receptor channels GluR1-GluR6 investigated in heterologous expression systems. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.