Role of Na+/H+ exchangers, excitatory amino acid receptors and voltage-operated Ca2+ channels in human immunodeficiency virus type 1 gp120-mediated increases in intracellular Ca2+ in human neurons and astrocytes

Human immunodeficiency virus type 1 (HIV-1) dementia is the commonest form of dementia in North American people less than 60 years of age. HIV-1 envel ope glycoprotein gp120 has been implicated in the neurotoxicity observed in , and the pathogenesis of, HIV-1 dementia. Recombinant gp120 (gp120) was pr essure-applied on to cultured human fetal neurons and astrocytes and, by us ing single-cell calcium imaging, we determined the mechanisms responsible f or gp120-induced increases in the levels of intracellular calcium ([Ca2+](i )). Significant dose-related increases in [Ca2+](i) were observed in neuron s and astrocytes. In neurons, 5 pM gp120 increased [Ca2+](i) by 290 +/- 13 nM and increases of 2210 +/- 211 nM were found at 209 nM, the highest conce ntration of gp120 tested. The apparent EC50 value for gp120 of 223 +/- 40 p M in neurons was not significantly different from that in astrocytes. Immun oelution of gp120 with polyclonal anti-gp120 and Ca2+-free conditions block ed increases in [Ca2+](i) by gp120. Increases in [Ca2+](i) were significant ly (P < 0.005) attenuated by the Na+/H+ exchange blocker 5-(N-methyl-N-isob utyl)-amiloride in neurons and astrocytes. The L-type calcium channel block ers nimodipine, diltiazem and CdCl2 + NiCl2 significantly (P < 0.005) reduc ed increases in [Ca2+](i) in neurons, but not astrocytes. Increases in [Ca2 +](i) by gp120 were not significantly affected by blockers of N-, P- and Q- type calcium channels. The N-methyl-D-aspartate receptor antagonists (+)-2- amino-5-phosphonopentanoic acid (AP5), memantine and dizocilpine significan tly (P < 0.01) lowered gp120-induced increases in [Ca2+](i) in neurons. AP5 and memantine, but not dizocilpine, significantly (P < 0.01) reduced incre ases in [Ca2+](i) by gp120 in astrocytes. Gp120 appears to activate astrocy te Na+/H+ exchangers to release glutamate and potassium and, subsequent to this, increases in [Ca2+](i) in neurons and astrocytes result from activati on of excitatory amino acid receptors on astrocytes and neurons, and voltag e-operated calcium channels on neurons. Drugs that block gp120-induced changes in [Ca2+](i) in neurons and astrocyt es may help in the treatment of HIV-1 dementia. (C) 1999 IBRO. Published by Elsevier Science Ltd.