HIV-1 ENVELOPE PROTEINS GP120 AND GP160 POTENTIATE NMDA-INDUCED [CA2+](I) INCREASE, ALTER [CA2+](I) HOMEOSTASIS AND INDUCE NEUROTOXICITY INHUMAN EMBRYONIC NEURONS

The envelope glycoprotein gp120 of the human immunodeficiency virus HI V-1 has been proposed to cause neuron death in developing murine hippo campal cultures and rat retinal ganglion cells. In the present study, cultured human embryonic cerebral and spinal neurons from 8- to 10-wee k-old embryos were used to study the neurotoxic effect of gp120 and gp 160. Electrophysiological properties as well as N-methyl-D-aspartate ( NMDA)induced currents were recorded from neurons maintained in culture for 10-30 days. Neither voltage-activated sodium or calcium currents nor NMDA-induced currents were affected by exposure of neurons to 250 pM gp120 or gp160. In contrast, when neurons were subjected to photome tric measurements using the calcium dye indo-1 to monitor the intracel lular free Ca2+ concentration ([Ca2+](i)), gp120 and gp160 (20-250 pM) potentiated the large rises in [Ca2+](i) induced by 50 mu M NMDA. The potentiation of NMDA-induced Ca2+ responses required the presence of Ca2+ in the medium, and was abolished by the NMDA antagonist D-2-amino -5-phosphonovalerate (AP5) and the voltage-gated Ca2+ channel inhibito r nifedipine. Moreover, exposure of a subpopulation of spinal neurons (25% of the cells tested) to 20-250 pM gp120 or gp160 resulted in an i ncrease in [Ca2+](i) that followed three patterns: fluctuations not af fected by AP5, a single peak, and the progressive and irreversible ris e of [Ca2+](i). The neurotoxicity of picomolar doses of gp120 and gp16 0 cultures was estimated by immunofluorescence and colorimetric assay. Treatment of cultures with AP5 or nifedipine reduced gp120-induced to xicity by 70 and 100% respectively.