Interactions of the dye Evans Blue and GYKI 52466, a 2,3-benzodiazepine, with (S)- alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors in cultured rat cortical neurons: electrophysiological evidence for at least two different binding sites for non-competitive antagonists.

The effects of the dye Evans Blue and GYKI 52466, a 2,3-benzodiazepine, on (S)- alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainate receptors in primary cultured rat cortical neurons were investigated using the patch-clamp technique. Evans Blue and GYKI 52466 reduced the currents induced by the application of 100 microM kainate with IC50 values of 10.6 +/- 1.4 microM and 12.1 +/- 0.4 microM, respectively. In contrast to the similar potencies of the two compounds, their kinetics of block were quite different with those of Evans Blue being more complex. The on-, as well as the off-reaction of the block by GYKI 52466 could be described by single exponential functions, whereas two different time-constants for binding and one time-constant for the unbinding of Evans Blue were found. The block of AMPA receptors by Evans Blue was not completely reversible under the experimental conditions applied in this study. GYKI 52466 was not able to augment the recovery after inhibiting AMPA receptors with Evans Blue. Moreover, preapplication of a high concentration of GYKI 52466 did not prevent the inhibition of AMPA receptors by Evans Blue. We therefore conclude that GYKI 52466 and Evans Blue bind to two different sites at AMPA receptors in primary cultured cortical neurons.