Binding of an AMPA receptor potentiator ([H-3]LY395153) to native and recombinant AMPA receptors

LY395153 is a member of a newly described class of arylpropylsulfonamide AM PA receptor potentiators. Here, we characterize and compare [H-3]LY395153 b inding to native AMPA receptors from rat cerebral cortex and recombinant hu man GluR4(flip) receptors expressed in HEK293 cells. L-Glutamate: and AMPA increased [H-3]LY395153 binding to both native and recombinant AMPA recepto rs in a concentration dependent and stereoselective manner; this effect of AMPA receptor agonists reflects an apparent increase in ligand affinity. In the presence of L-glutamate (500 muM), [H-3]LY395153 binding is saturable; the affinity of this radioligand is slightly, albeit statistically signifi cantly higher at human GluR4(flip) (K-d=55.6 +/-5.3nM) than rat cortical re ceptors (K-d=110 +/- 15.1nM). NBQX competitively inhibited L-glutamate-indu ced increases in [H-3]LY395153 binding in both native and recombinant recep tors, whilst LY303070 (the active isomer of GYKI53655) noncompetitively inh ibited this effect in native, but not recombinant receptors. The prototypic AMPA receptor potentiator cyclothiazide competitively inhibited [H-3]LY395 153 binding with a potency (K(i)similar to7 muM) comparable to EC,, values reported in electrophysiological studies. In contrast, the structurally unr elated AMPA receptor potentiator CX 516 did not inhibit [H-3]LY395153 bindi ng at concentrations of up to 600 muM. Further, at concentrations reported to facilitate AMPA receptor desensitization, thiocyanate acts as a competit ive inhibitor of [H-3]LY395153 binding. [H-3]LY395153 binding was unaffecte d by a variety of structurally land mechanistically) diverse compounds test ed at a concentration of 10 muM. These data indicate [H-3]LY395153 is a use ful probe for labeling a unique modulatory site on both native and recombin ant AMPA receptors. (C) 2001 Elsevier Science Ltd. All rights reserved.