THE EFFECTS OF COPPER IONS ON GLUTAMATE RECEPTORS IN CULTURED RAT CORTICAL-NEURONS

Copper plays an important role in the function of many physiological p rocesses and can affect different neurotransmitter systems. In this st udy, we used the patch-clamp technique to investigate the effect of co pper ions on glutamate receptors in cultured rat cortical neurons. CU2 + inhibited lpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (A MPA)/kainate receptors with an IC50 of 4.3 +/- 0.6 mu M (with 100 mu M kainate, holding potential -60 mV). The concentration-response could be best described by a two-site binding model. Moreover, copper reduce d the efficacy of kainate at the AMPA receptor: in the presence of 30 mu M Cu2+, the EC(50) of kainate was shifted from 100.3 +/- 2.0 mu M t o 329.9 +/- 31.4 mu M. The block by copper ions was not use-dependent. Complete recovery only occurred after the application of a high agoni st concentration, or in the presence of the antioxidant dithiotreitol (DTT). A high concentration of histidine, a physiological ligand for C u2+, did not augment the recovery. The kinetics of block were compared to those induced by 2,3-dihydro-6-nitro-7-sulfamoyl-benz(F)quinoxalin e (NBQX), a well-described competitive antagonist of AMPA receptors. T he onset, as well. as the offset of block by NBQX could be well approx imated 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 kin etics of copper block were more complex: the block developed more slow ly, and the onset, as well as the offset could be described by two exp onential functions with quite different time constants (tau(on1), 0.8 +/- 0.13 s; tau(on2), 8.32 +/- 1.13 s; tau(off1), 0.17 +/- 0.01 s; tau (off2), 69 +/- 36.3 s). In addition to the described effects, Cu2+ als o blocked currents induced by the application of N-methyl-D-aspartate (IC50: 15.0 +/- 2.6 mu M with 50 mu M NMDA). Based on these findings, a modulatory role of copper ions on the neurotransmission by excitator y amino acids is discussed.