Journal archive > 2011 > N 2 March-April 

EXOCYTOTIC STEPS IN CELL-FREE SYSTEM AFTER CHOLESTEROL DEPRIVATION
IN SYNAPTOSOMAL PLASMA MEMBRANES AND SYNAPTIC VESICLES

V. P. Gumenyuk, I. O. Trikash

Palladin Institute of Biochemistry, National Academy of Sciences of Ukraine, Kyiv;
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Using a cell-free system we investigated a specific role of cholesterol in exocytotic processes. To modulate the cholesterol content in membrane methyl-?-cyclodextrin was used as a cholesterol binding agent. The experimental conditions for cholesterol depletion from synaptosomal membrane structures were determined and depended on methyl-?-cyclodextrin concentration, time and mediums temperature. The role of cholesterol was studied on the stages of synaptic vesicles docking and Ca2+-stimulated fusion which are the components of multivesicular compound exocytosis. Using­ dynamic light scattering technique we have found that after cholesterol depletion from synaptic vesicles the process of their aggregation (docking) remains unchanged.
It was found that the rate of calcium-triggered fusion of synaptic vesicles depends on the membrane level of cholesterol. The decreasing level of synaptosomal plasma membrane cholesterol by 8% leads to suppression of the Ca2+-dependent membrane fusion with synaptic vesicles. But, under 25% reduction of plasma membrane cholesterol the level­ of membrane merging with synaptic vesicles did not differ from control; probably this is due to changes in physical properties of lipid bilayer and/or disturbances in function of membrane proteins driving this process.
In cholesterol depleted synaptosomes the exocytotic release of glutamate stimulated by calcium was decreased by 32%. Obtained data suggest that the cholesterol concenration in synaptosomal plasma membranes or synaptic vesicles is the crucial determinant for synaptic transmission efficiency in nerve terminals.

Key words: exocytosis, membrane fusion, cholesterol, synaptic vesicles, synaptosomes.

The original article in Ukrainian is available for download in PDF format.

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