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Measurement of Total Calcium in Neurons by Electron Probe X-ray Microanalysis
Published on: November 21, 2013
HIV-1 envelope protein evokes intracellular calcium oscillations in rat hippocampal neurons
T M Lo1, C J Fallert, T M Piser
1Department of Pharmacology, University of Minnesota Medical School, Minneapolis 55455.
Insights
HIV-1 envelope glycoprotein gp120 increases intracellular calcium in rat hippocampal neurons. This excitotoxicity involves calcium and sodium channels, and N-methyl-D-aspartate receptors, potentially impacting neuronal network activity.
Area of Science:
- Neuroscience
- Neurovirology
- Cellular Physiology
Background:
- HIV-1 infection can affect the central nervous system.
- The HIV-1 envelope glycoprotein gp120 is implicated in neurotoxicity.
- Understanding gp120's effects on neurons is crucial for addressing neurological complications of HIV/AIDS.
Purpose of the Study:
- To investigate the effects of HIV-1 gp120 on intracellular calcium concentration ([Ca2+]i) in rat hippocampal neurons.
- To characterize the patterns of [Ca2+]i changes induced by gp120.
- To elucidate the ion channel and receptor mechanisms underlying gp120-induced [Ca2+]i alterations.
Main Methods:
- Primary culture of rat hippocampal neurons.
- Indo-1-based microfluorimetry to measure intracellular free calcium concentration ([Ca2+]i).
- Application of recombinant HIV-1 gp120 and pharmacological agents (nitrendipine, CGS19755, tetrodotoxin).
Main Results:
- Treatment with gp120 caused significant increases in [Ca2+]i, exhibiting single peaks or oscillations.
- Both single-peak and oscillatory [Ca2+]i increases were blocked by the calcium channel blocker nitrendipine.
- Sustained oscillatory responses were reversibly blocked by NMDA receptor antagonist CGS19755 and sodium channel blocker tetrodotoxin.
- Complete blockade by channel antagonists suggests a network-dependent mechanism involving at least two cells.
Conclusions:
- HIV-1 gp120 induces alterations in intracellular calcium dynamics in hippocampal neurons.
- gp120-induced calcium responses are mediated by calcium and sodium channels, as well as NMDA receptors.
- The findings support the hypothesis that gp120 acts as an excitotoxin, potentially through increased synaptic activity in neuronal networks.
Abstract:
Treatment of single rat hippocampal neurons with 200 pM recombinant HIV-1 envelope glycoprotein, gp120, resulted in large increases in the intracellular free calcium concentration ([Ca2+]i) as measured with indo-1-based microfluorimetry. Three patterns of [Ca2+]i increases were observed: in one pattern the [Ca2+]i rose rapidly and transiently as a single peak, in a second pattern gp120 induced [Ca2+]i oscillations that subsided when the protein was removed, and in a third pattern the oscillations continued long after washout of gp120. Both single peak and oscillatory [Ca2+]i increases were completely blocked by the Ca2+ channel blocker nitrendipine (1 microM). The sustained oscillatory responses were also blocked completely and reversibly by the N-methyl-D-aspartate (NMDA) receptor antagonist CGS19755 (10 microM) and the Na+ channel blocker tetrodotoxin (1 microM). Complete block by antagonists of Ca2+, Na+, and NMDA-gated ion channels suggests that at least two cells are required to maintain the [Ca2+]i oscillations. We hypothesize that gp120 acts as an excitotoxin by increasing synaptic activity in the network of neurons established in primary culture.
