Developmental change of the inhibition by lead of NMDA-activated currents in cultured hippocampal neurons
Ujihara, H.; Albuquerque, E.X.
Journal of Pharmacology and Experimental Therapeutics 263(2): 868-875
1992
ISSN/ISBN: 0022-3565 PMID: 1432703 Document Number: 398711
The inhibition of N-methyl-D-aspartate (NMDA)-activated current in cultured fetal rat hippocampal neurons by Pb-2+ was investigated at various stages of cell development. Pb-2+ selectiviely inhibited NMDA current recorded from young cultured neurons. In the first week of culture, Pb-2+ showed the most prominent inhibition, which was gradually attenuated in the following weeks. Pb-2+'s action was selective for NMDA- as opposed to either kainate- or quisqualate-induced currents. The current-voltage relationship for NMDA-induced currents in the presence of Pb-2+ revealed that the effect of this cation was voltage-independent, which suggested that the site of interaction of Pb-2+ with the NMDA receptor/channel is located outside the membrane electric field. Single channel studies showed that Pb-2+ reduced the frequency but not the lifetime of the NMDA-activated single channel currents. Further evaluation of the mechanism of action of Pb-2+ on the NMDA receptor demonstrated that this cation is a noncompetitive antagonist of both NMDA and glycine. We have demonstrated that the NMDA-induced whole cll currents change along with cell development, and the effects of Pb-2+ are also dependent upon age of culture. The NMDA-induced currents in cultured rat hippocampal neurons had two components, one that decayed rapidly and another that decayed slowly. The fast component was clearly observed at concentrations of glycine higher than 1 mu-M, whereas the slow component reached its maximum amplitude at the glycine concentration of 1 mu-M. Moreover, the rapidly decaying component of NMDA-evoked whole cell currents was predominant in young cultured neurons, and its contribution to the total current was reduced in old cultured neurons. Pb-2+ inhibited preferentially the fast component of the NMDA-evoked whole cell currents. These findings on the action of Pb-2+ at the NMDA receptor may explain the selective toxicity of this heavy metal on the immature brain.