Effects of cyclothiazide on GluR1/AMPA receptors

Cyclothiazide (CTZ), a positive allosteric modulator of ionotropic alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)type glutamate receptors, is used frequently to block the desensitization of both native and heterologously expressed AMPA receptors. Specifically, CTZ is known to produce a fast inhibition of AMPA receptor desensitization and a much slower potentiation of the AMPA current. By using patch-clamp techniques, the effects of CTZ were studied in HEK 293 cells stably transfected with the rat flip GluR1 subunit. Upon CTZ treatment, we found an increased apparent affinity for the agonist, a slow whole-cell current potentiation, a fast inhibition of desensitization, and a lengthening of single-channel openings. Furthermore, we show that CTZ alters the channel gating events modifying the relative contribution of different single-channel classes of conductance (gamma), increasing and decreasing, respectively, the contributions of gamma(M) (medium) and gamma(L) (low) without altering that of the gamma(H) (high) conductance channels. We also present a kinetic model that predicts well all of the experimental findings of CTZ action. Finally, we suggest a protocol for standard cell treatment with CTZ to attain maximal efficacy of CTZ on GluR1 receptors.