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Caveolin-1 expression and membrane cholesterol content modulate N-type calcium channel activity in NG108-15 cells
M Toselli1, G Biella, V Taglietti
1Department of Cellular and Molecular Physiological and Pharmacological Sciences, and INFM (National Institute of Matter Physics), University of Pavia, Pavia, Italy.
Biophysical Journal
|July 26, 2005
Summary
Caveolin-1 expression reduces neuronal calcium channel activity by increasing membrane cholesterol. This finding suggests caveolin-1 plays a role in regulating neuronal excitability through lipid-mediated mechanisms.
Area of Science:
- Neuroscience
- Cell Biology
- Biochemistry
Background:
- Caveolins are structural proteins of caveolae, involved in membrane remodeling and cholesterol transport.
- Caveolin-1 is found in hippocampal neurons and forms complexes with SNAP25 after synaptic potentiation.
- NG108-15 cells, lacking endogenous caveolins, express N-type Ca2+ channels upon differentiation.
Purpose of the Study:
- To investigate the effect of caveolin-1 on basal activity of neuronal voltage-gated Ca2+ channels.
- To determine if caveolin-1 influences N-type Ca2+ channel current density.
- To elucidate the mechanism by which caveolin-1 affects Ca2+ channel activity, specifically the role of membrane cholesterol.
Main Methods:
- Stable expression of caveolin-1 in NG108-15 hybrid cells (cav1(+) clone).
- Whole-cell patch-clamp recordings to measure N-type Ca2+ channel current density, activation, inactivation, and voltage dependence.
- Analysis of membrane cholesterol content.
- Single N-type channel recordings in cav1(+) and wild-type cells after cholesterol enrichment using methyl-beta-cyclodextrin-cholesterol complex.
Main Results:
- Caveolin-1 expression significantly reduced N-type Ca2+ current density by approximately 70% without altering channel kinetics or voltage dependence.
- Cav1(+) cells showed a higher proportion of membrane cholesterol compared to wild-type cells.
- Cholesterol enrichment in both cell types mimicked the effect of caveolin-1, reducing Ca2+ channel activity.
- Reduced Ca2+ channel activity was attributed to decreased opening probability, shorter mean open time, and increased null sweeps.
Conclusions:
- Caveolin-1 expression lowers neuronal N-type Ca2+ channel activity.
- Increased membrane cholesterol is the primary mechanism underlying caveolin-1's effect on Ca2+ channel function.
- Caveolin-1 influences neuronal excitability by modulating Ca2+ channel activity through cholesterol-dependent mechanisms.