Glycine and calcium-dependent effects of lead on N-methyl-D-aspartate receptor function in rat hippocampal neurons.
The effects of lead (Pb++) on N-methyl-D-aspartate (NMDA) receptor function of rat hippocampal neurons in culture were studied by use of the whole-cell patch-clamp technique. Currents activated by NMDA (100 microM) in the presence of nonsaturating concentrations of glycine (0.01-0.05 microM) were potentiated in a voltage-independent manner by Pb++ (1-10 microM), and the potentiation was antagonized by 50 microM kynurenic acid. Increasing extracellular Ca++ from 1 to 10 mM similarly potentiated the NMDA-activated currents in the presence of a nonsaturating concentration of glycine (0.2 microM). The potentiation of NMDA-activated currents by low micromolar concentrations of Pb++ may be mediated by this cation's ability to increase the affinity of the NMDA receptor for glycine. In the presence of 10 microM glycine and 2 mM Ca++, Pb++ reduced the peak amplitudes of currents activated by NMDA (100 microM) in a voltage-independent manner (IC50 = 5.9 microM Pb++, Hill coefficient (nH) = 1.2). Also, steady-state currents activated by NMDA (50 microM) were inhibited by rapid application of Pb++ (IC50 = 3.2 microM, nH = 0.7). Increasing extracellular Ca++, in the presence of 10 microM glycine, reduced the NMDA-activated currents and shifted the Pb++ concentration-response curves to the right: at 0.2, 2 and 20 mM Ca++, the IC50 values of Pb++ were 3.0, 5.9 and 12.5 microM and the nH values were 0.9, 1.2 and 1.1, respectively. The finding that external Ca++ antagonized the inhibitory effect of Pb++ suggests that the noncompetitive inhibitory action of Pb++ with respect to glycine and NMDA may be mediated by Pb++ competition with Ca++ for a site on the NMDA receptor.
Marchioro
M
M
Department of Pharmacology and Experimental Therapeutics, University of Maryland School of Medicine, Baltimore, USA.
Swanson
K L
KL
Aracava
Y
Y
Albuquerque
E X
EX
D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000494:pharmacology*; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D005998:Glycine / Q000494:pharmacology*; D006624:Hippocampus / Q000187:drug effects* / Q000502:physiology; D007736:Kynurenic Acid / Q000494:pharmacology; D007854:Lead / Q000378:metabolism / Q000633:toxicity*; D016202:N-Methylaspartate / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D016194:Receptors, N-Methyl-D-Aspartate / Q000187:drug effects* / Q000502:physiology
D016194:Receptors, N-Methyl-D-Aspartate; D007854:Lead; D016202:N-Methylaspartate; D007736:Kynurenic Acid; D002118:Calcium; D005998:Glycine