Cyclothiazide decreases [3H]AMPA binding to rat brain membranes: evidence that AMPA receptor desensitization increases agonist affinity.

The effects of cyclothiazide, a drug which blocks AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) receptor desensitization, were tested on binding of [3H]AMPA to rat brain membranes. Cyclothiazide reduced [3H]AMPA binding by lowering the apparent affinity of the AMPA receptor. The magnitude of the decrease was temperature dependent and greater for membrane-bound than for solubilized receptors. These data provide evidence that desensitization increases the affinity of the AMPA receptor for agonists and indicate that a significant percentage of AMPA receptors in conventional equilibrium binding assays are in a desensitized state.