Ishihara K, Alkondon M, Montes J G, Albuquerque E X
Department of Pharmacology and Experimental Therapeutics, University of Maryland School of Medicine, Baltimore, USA.
J Pharmacol Exp Ther. 1995 Jun;273(3):1459-70.
The sensitivity of N-methyl-D-aspartate- (NMDA) induced whole-cell and single-channel currents to Pb2+ was studied in neurons acutely dissociated from the hippocampus of 3- to 30-day-old rats. The amplitude of NMDA-induced whole-cell currents in the neurons increased with age of the animals until they were 10 to 12 days old, thereafter remaining nearly unchanged. As in cultured hippocampal neurons, Pb2+ at both 10 and 30 microM inhibited NMDA-induced currents, and the sensitivity of the currents to Pb2+ decreased with age of the rats. The sensitivity correlated with the age-related expression of two components of the NMDA-induced currents, one that was fast decaying and more prominent in younger neurons, and the other slowly decaying. Inhibition of the fast component by Pb2+ was always greater than that of the slow component, which may explain the greater sensitivity of younger neurones to Pb2+. may explain the greater sensitivity of younger neurons to Pb2+. The use of trypsin during acute dissociation of the neurons did not qualitatively alter the findings, although in the trypsin-treated neurons the currents were 65% smaller, and the EC50 for NMDA and glycine for the slow component were both about two times greater than in the untreated neurons; in the case of the fast component, the EC50s for NMDA and for glycine were not significantly altered. In outside-out patches excised from acutely dissociated hippocampal neurons, Pb2+ decreased the frequency of NMDA-activated channel openings without altering the mean channel open time. Our results are in agreement with those reported for embryonic neurons that developed in culture, and indicate that NMDA receptors expressed in hippocampal neurons of young animals are key target sites for the neurotoxic actions of Pb2+.
在从3至30日龄大鼠海马中急性分离出的神经元中，研究了N-甲基-D-天冬氨酸（NMDA）诱导的全细胞电流和单通道电流对Pb2+的敏感性。神经元中NMDA诱导的全细胞电流幅度随动物年龄增加而增大，直至10至12日龄，此后几乎保持不变。与培养的海马神经元一样，10 microM和30 microM的Pb2+均抑制NMDA诱导的电流，且电流对Pb2+的敏感性随大鼠年龄增长而降低。这种敏感性与NMDA诱导电流的两个成分的年龄相关表达有关，一个成分快速衰减且在较年轻神经元中更突出，另一个成分缓慢衰减。Pb2+对快速成分的抑制总是大于对缓慢成分的抑制，这可能解释了较年轻神经元对Pb2+更敏感的原因。在神经元急性分离过程中使用胰蛋白酶并未定性改变研究结果，尽管在经胰蛋白酶处理的神经元中电流小65%，且缓慢成分的NMDA和甘氨酸的半数有效浓度（EC50）均约为未处理神经元的两倍；对于快速成分，NMDA和甘氨酸的EC50没有显著改变。在从急性分离的海马神经元上切下的外向型膜片中，Pb2+降低了NMDA激活通道开放的频率，而不改变平均通道开放时间。我们的结果与报道的在培养中发育的胚胎神经元的结果一致，表明幼龄动物海马神经元中表达的NMDA受体是Pb2+神经毒性作用的关键靶点。
