부산대학교 도서관

Copper plays an important role in the function of many physiological processes and can affect different neurotransmitter systems. In this study, we used the patch-clamp technique to investigate the effect of copper ions on glutamate receptors in cultured rat cortical neurons. Cu2+inhibited (S)-α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainate receptors with an IC50of 4.3 ± 0.6 μM (with 100 μM kainate, holding potential −60 mV). The concentration-response could be best described by a two-site binding model. Moreover, copper reduced the efficacy of kainate at the AMPA receptor: in the presence of 30 μM Cu2+, the EC50of kainate was shifted from 100.3 ± 2.0 μM to 329.9 ± 31.4 μM. The block by copper ions was not use-dependent. Complete recovery only occurred after the application of a high agonist concentration, or in the presence of the antioxidant dithiotreitol (DTT). A high concentration of histidine, a physiological ligand for Cu2+, did not augment the recovery. The kinetics of block were compared to those induced by 2,3-dihydro-6-nitro-7-sulfamoyl-benz(F)quinoxaline (NBQX), a well-described competitive antagonist of AMPA receptors. The onset, as well as the offset of block by NBQX could be well approximated by single exponential functions with time constants of 0.28 ± 0.02 and 0.87 ± 0.09 s, respectively. Within seconds of wash-out of the antagonist, the response to kainate completely recovered. The kinetics of copper block were more complex: the block developed more slowly, and the onset, as well as the offset could be described by two exponential functions with quite different time constants (τon1, 0.8 ± 0.13 s; τon2, 8.32 ± 1.13 s; τoff1, 0.17 ± 0.01 s; τoff2, 69 ± 36.3 s). In addition to the described effects, Cu2+also blocked currents induced by the application of N-methyl-d-aspartate (IC50: 15.0 ± 2.6 μM with 50 μM NMDA). Based on these findings, a modulatory role of copper ions on the neurotransmission by excitatory amino acids is discussed.