Blockade of AMPA receptors by nickel in cultured rat astrocytes

The effect of Ni2+ on glial alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptors was studied using the whole-cell patch-clamp technique in cultured rat cerebellar astrocytes. The application of kainate (10 mu M-5 mM) evoked inward currents at a holding potential of -70 mV. These currents were blocked by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and Evans Blue, and potentiated by cyclothiazide, suggesting that they were primarily mediated by the AMPA receptor subtype. Analysis of the kainate concentration-response relation in cultured astrocytes revealed a maximal current of 488 pA, a half-maximal effective concentration of 137 mu M and a Hill coefficient of 1.43, indicating more than one agonist binding site. Ni2+ inhibited the current activated by 300 mu M kainate in a concentration-dependent manner, displaying a half-maximal inhibition at 860 mu M Ni2+ and a Hill coefficient of 1.07. In the presence of 700 mu M Ni2+ the kainate-induced concentration-response curve was shifted towards higher concentrations, increasing the half-maximal effective concentration to 300 mu M, without significantly changing the Hill coefficient. The blocking effect of Ni2+ was counteracted by increasing kainate concentrations, suggesting a competitive mechanism. (C) 1996 Wiley-Liss, Inc.