Excitatory effects of human immunodeficiency virus 1 Tat on cultured rat cerebral cortical neurons

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• 作者：G.C. Brailoiu ; E. Brailoiu ; J.K. Chang ; N.J. Dun
• 关键词：calcium imaging ; electrophysiology ; postsynaptic currents
• 刊名：Neuroscience
• 出版年：2008
• 期刊代码：50_03064522
• 类别：neu
• 出版时间：6 February 2008
• 卷：151
• 期：3
• 页码：701-710
• 文件大小：851 K

摘要

Human immunodeficiency virus 1 (HIV-1) Tat protein is one of the neurotoxins involved in the pathogenesis of HIV-1-associated neuronal disorders. Combined electrophysiological and optical imaging experiments were undertaken to investigate whether HIV-1 Tat30-86, herein referred to as Tat30-86, acted directly or indirectly via the release of glutamate or both and to test its effect on the properties of spontaneous quantal events in cultured cortical neurons. Whole-cell patch recordings were made from cultured rat cortical neurons in either current- or voltage-clamp mode. Tat30-86 (50–1000 nM) induced in a population of cortical neurons a long-lasting depolarization, which was accompanied by a decrease of membrane resistance and persisted in a Krebs solution containing tetrodotoxin (TTX, 0.5 μM). Depolarizations were slightly reduced by pretreatment with glutamate receptor antagonists 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) (10 μM) and d-2-amino-5-phosphonovaleric acid (AP-5) (50 μM), and were markedly reduced in a Ca²⁺-free Krebs solution; the differences were statistically significant. Tat30-86-induced inward currents had a reversal potential between −30 and 0 mV. While not causing a noticeable depolarization, lower concentrations of Tat30-86 (10 nM) increased membrane excitability, as indicated by increased numbers of neuronal discharge in response to a step depolarizing pulse. Tat30-86 (10 nM) increased the frequency of spontaneous miniature excitatory postsynaptic currents (mEPSCs), while not significantly affecting their amplitude. Tat30-86 (10 nM) moderately increased the frequency as well as the amplitude of spontaneous miniature inhibitory postsynaptic currents (mIPSCs). Ratiometric Ca²⁺ imaging studies showed that Tat30-86 produced three types of Ca²⁺ responses: 1) a fast and transitory increase, 2) Ca²⁺ oscillations, and 3) a fast increase followed by a plateau; the glutamate receptor antagonists eliminated the late component of Ca²⁺ response. The result suggests that Tat30-86 is an active fragment and that it excites cortical neurons directly and indirectly via releasing glutamate from adjacent neurons.