Tag Archives: exocytosis

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;
e-mail: trikash@biochem.kiev.ua

Using a cell-free system we investigated a specific role of cholesterol in exocytotic processes. To modulate the cholesterol content in membrane methyl-β-cyclodextrin was used as a cholesterol binding agent. The experimental conditions for cholesterol depletion from synaptosomal membrane structures were determined and depended on methyl-β-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.

Activation of presynaptic ionotropic glutamate receptors stimulates gaba release from hippocampal and cortical rat brain nerve terminals

O. О. Krupko, A. S. Tarasenko, N. G. Himmelreich

Palladin Institute of Biochemistry, National Academy
of Sciences of Ukraine, Kyiv;
e-mail: olya_krupko@mail.ru

One of the pathways implicated in a fine-tuning control of neurosecretory process is the activation of presynaptic receptors. The present study was focused on the role of presynaptic glutamate receptor activation in the regulation of inhibitory synaptic transmission in the rat hippocampus and cortex. We aimed to clarify what types of ionotropic glutamate receptors are involved in the modulation of GABA secretion, and what mechanism underlies this modulation. We have revealed that specific agonists of kainate and NMDA receptors, kaina­te and NMDA, like glutamate, induced the release of [3H]GABA from hippocampal and cortical nerve terminals suggesting the involvement of both types in the regulation of GABAergic transmission. Our results indicate preferential involvement of vesicular, but not cytosolic, pool in response to glutamate receptor activation. This is based on the finding that NO-711 (a specific inhibitor of plasma membrane GABA transporters), fails to attenuate [3H]GABA release. We have concluded that presynaptic glutamate receptor-induced modulation of the strength of synaptic response is due to increasing the release probability of synaptic vesicles.