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.
Telgkamp
P
P
Abteilung fur Allgemeine Zoologie, Universitat Kaiserslautern, Germany.
Backus
K H
KH
Deitmer
J W
JW
D000818:Animals; D000831:Animals, Newborn; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002478:Cells, Cultured; D003470:Culture Media; D004594:Electrophysiology; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism; D007608:Kainic Acid / Q000494:pharmacology; D009532:Nickel / Q000494:pharmacology*; D018408:Patch-Clamp Techniques; D051381:Rats; D018091:Receptors, AMPA / Q000037:antagonists & inhibitors* / Q000378:metabolism; D018092:Kainic Acid Receptors / Q000037:antagonists & inhibitors
D003470:Culture Media; D018690:Excitatory Amino Acid Agonists; D018691:Excitatory Amino Acid Antagonists; D007473:Ion Channels; D007608:Kainic Acid; D009532:Nickel; D018091:Receptors, AMPA; D018092:Kainic Acid Receptors