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 envelope glycoprotein gp120 has been implicated in the neurotoxicity observed in, and the pathogenesis of, HIV-1 dementia. Recombinant gp120 (gp120) was pressure-applied on to cultured human fetal neurons and astrocytes and, by using single-cell calcium imaging, we determined the mechanisms responsible for gp120-induced increases in the levels of intracellular calcium ([Ca2+]i). Significant dose-related increases in [Ca2+]i were observed in neurons 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 concentration of gp120 tested. The apparent EC50 value for gp120 of 223+/-40 pM in neurons was not significantly different from that in astrocytes. Immunoelution of gp120 with polyclonal anti-gp120 and Ca2+-free conditions blocked increases in [Ca2+]i by gp120. Increases in [Ca2+]i were significantly (P < 0.005) attenuated by the Na+/H+ exchange blocker 5-(N-methyl-N-isobutyl)-amiloride in neurons and astrocytes. The L-type calcium channel blockers nimodipine, diltiazem and CdCl2 + NiCl2 significantly (P < 0.005) reduced 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 significantly (P < 0.01) lowered gp120-induced increases in [Ca2+]i in neurons. AP5 and memantine, but not dizocilpine, significantly (P < 0.01) reduced increases in [Ca2+]i by gp120 in astrocytes. Gp120 appears to activate astrocyte Na+/H+ exchangers to release glutamate and potassium and, subsequent to this, increases in [Ca2+]i in neurons and astrocytes result from activation of excitatory amino acid receptors on astrocytes and neurons, and voltage-operated calcium channels on neurons. Drugs that block gp120-induced changes in [Ca2+]i in neurons and astrocytes may help in the treatment of HIV-1 dementia.
Holden
C P
CP
Department of Pharmacology and Therapeutics, University of Manitoba Faculty of Medicine, Winnipeg, Canada.
Haughey
N J
NJ
Nath
A
A
Geiger
J D
JD
D001253:Astrocytes / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000502:physiology*; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D005333:Fetus / Q000166:cytology; D015699:HIV Envelope Protein gp120 / Q000494:pharmacology / Q000502:physiology*; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism*; D017459:Receptors, Amino Acid / Q000502:physiology*; D011994:Recombinant Proteins; D017923:Sodium-Hydrogen Exchangers / Q000502:physiology*
D015220:Calcium Channels; D015699:HIV Envelope Protein gp120; D017459:Receptors, Amino Acid; D011994:Recombinant Proteins; D017923:Sodium-Hydrogen Exchangers; D002118:Calcium