Vesicles diameter

Synaptic vesicles are the organelles in axon terminals that store neurotransmitters and release them by exocytosis. There are two types, the large dense-core vesicles, diameter about 90 nm, that contain neuropeptides, and the small synaptic vesicles, diameter about 50nm, that contain non-peptide transmitters. About ten vesicles per synapse are docked to the plasma membrane and ready for release, the readily releasable pool . Many more vesicles per synapse are stored farther away from the plasma membrane, the resting pool . When needed, the latter vesicles may be recruited into the readily releasable pool. Neuronal depolarization and activation of voltage-sensitive Ca2+... 

FIGURE18-4 Neuropeptides and conventional neurotransmitters are released from different parts of the nerve terminal. A neuromuscular junction containing both large dense-core vesicles (containing the neuropeptide SCP) and also small synaptic vesicles (containing acetylcholine) was stimulated for 30 min at 12 Hz (3.5 s every 7 s). Depletion of the small clear vesicles at the muscle face and of the peptide granules at the nonmuscle face of the nerve terminal was observed. After stimulation, there was an increase in the number of large dense-core vesicles within one vesicle diameter of the membrane. (Adapted from reference [37].)... 

The final surfactant structures we consider as models for biological membranes are vesicles. These are spherical or ellipsoidal particles formed by enclosing a volume of aqueous solution in a surfactant bilayer. When phospholipids are the surfactant, these are also known as liposomes, as we have already seen in Vignette 1.3 in Chapter 1. Vesicles may be formed from synthetic surfactants as well. Depending on the conditions of preparation, vesicle diameters may range from 20 nm to 10 pirn, and they may contain one or more enclosed compartments. A multicompartment vesicle has an onionlike structure with concentric bilayer surfaces enclosing smaller vesicles in larger aqueous compartments. 

Fig. 51 a—c. Phase-contrast photographs of a fusion of large unilamellar vesicles (LUVs) prepared from a 1 1 mixture of (26) and cholesterol. Vesicle diameters 37 and 45 pm, respectively, a) orientation in an ac field of about 2 kV/cm b) elongated fused liposome, one second after application of a 30 ps, 140 V/cm field pulse c) spherical new vesicle after turning off ac field new diameter 51 pm83)... 

One of the peculiarities of reactions in suspensions of vesicles is the possibility of obtaining a much higher local concentration of reagents located in membranes or the inner cavity than their average concentration in suspension. For instance, the presence of one molecule in the inner cavity of a DPL vesicle (diameter 220 A, membrane thickness 50 A [40]) corresponds to the local concentration of about 3 x 10 3 mol/1. These values correspond to only about 10 6 mol/1 average concentration of the same species in the suspension containing 3 x 10 3 mol/1 of the DPL lipid, since the overall volume of the vesicle cavities in such suspensions... 

Fig. 3.30 Resonance of glycolic acid before (a) and after (b) addition of PrCI3 as shift reagent to the vesicle system, pH 3.94, 30 °C, 100 nm vesicle diameter. (Reprinted from Fig. 2 of ref. 11 7 with permission from Elsevier Science.)...

Generation dendrimer Vesicle diameter (nm) from EM Vesicle diameter (nm) from DLS" CAC (pM) Bilayer thickness (nm) Molecular area (nm ) ... 

Minimum vesicle diameters obtained afrer 10 cycles of microfluidization are about 100-160 nm, depending on whether microfluidization was carried out in H O or PB, using unwashed or washed liposomes. 

Homogeneous in size vesicle dispersions can be achieved through vortexing, freeze-thaw cycles, extrusion and sonication, or a combination of these methods. These steps usually also lead to decrease of vesicle diameter and lamellarity [101,157],... 

The effective area of interaction is taken to be the area subtended by the surface of the vesicle between a closest approach to one water-molecule diameter and two such diameters. This area will be 5 X 10 /im for a vesicle diameter of 4 x 10 fim. 

Figure 1. Video micrographs of an adhesion test, (a) Vesicles in position for contact, (u) Adhesion - equilibrium controlled by tne suction pressure. (Pipet calibre- 1 x i0 cm vesicle diameters 2 x lQ cm).

Controllable vesicle diameter, degradability, stability in presence of serum proteins ... 

Fig. 21 Schematic of AFM tip-assisted immobilization drawn approximately to scale (bUayer thickness 4nm tip radius 20 nm vesicle diameter 40nm) a An intact defect-free DMPC bilayer is formed on a mercaptoethanol SAM on gold (SAM is omitted from schematic) b subsequent scanning with an AFM tip at high force leads to local damage of the bilayer c in these areas (the schematic drawing does not imply any molecular detail concerning the damage created in step (b)) vesicles wiU adsorb from the solution and stay immobilized. (Reprinted with permission from [174], copyright (2004), American Chemical Society)...

PMAA was hydrophobically modified with stearyl or lauryl methacrylate and the interactions of these modified polymers with PC/cholesterol membranes were investigated by dynamic light scattering, calorimetry and fluorescence anisotropy. Vesicle diameter was observed to increase in the presence of polymer from -180 nm in the absence of polymer to -240nm at 10 wt.%. Vesicles containing 8 2 PC-Chol showed a relatively sharp transition at 51 °C that split into two peaks (51 C and - 46 ° C) at 10 wt.% polymer and then became one peak again at -44 C at 40 wt.% polymer. Meanwhile, 6 4 PC-Chol vesicles showed only a broad transition that sharpened at 40 wt.% polymer to a peak centered - 42 C. Lairryl-suhstituted copolymers showed more lipid-lipid disraption than stearyl substituted ones. 

Tsuchida has developed a very elegant approach based on the use of amphiphilic porphyrins in which the lipophilic moiety of the amphiphile is the porphyrin and the polar head group is a classical phospholipid moiety The compounds 125(M) represented in Figure 13.66 are able to form vesicles containing up to 23,000 porphyrins (vesicle diameter 100-150 nm). This is without a doubt the largest structurally characterized multiporphyrinic assembly characterized to date. 

The reduction in viscosity observed with PAA is much greater due to the screening of the intra- and inter-lamellar electrostatic rq>ulsion. The water layer thickness of the vesicles is controlled by the electrostatic repulsion between SDS molecules in opposite bilayers and the addition of electrolyte screens this repulsion. This effect contributes to the reduction in vesicle diameter caused by the osmotic compression. 

The effect of water-soluble polymers on the properties of dilute lamellar dispersions was studied and the primary effect was found to be due to the exclusion of polymer from the water layers. This exclusion results in an osmotic compression of the water layers and a reduction in the vesicle diameter, phase volume, and dispersion viscosity. Depletion flocculation leads to fusion and morphological changes in the dispersion. Polyelectrolytes screen the electrostatic repulsion between bilayers and vesicles and this effect is superimposed on the osmotic compression. There was no apparent direct interaction between the polymmrs and the bilayers observed. 

I. Clathrin-eoated vesicle a transport vesicle, diameter about 800 A, formed in the process of endocy-tosis (pinocytosis), and found in vinually all eukaryotic cells. A C-c.v. is therefore also an endocytic or pi-nocytic vesicle. A C-c. v. is formed by invagination of a coated pit in the plasma membrane. A coated pit is a highly specialized region of the plasma membrane carrying cell surface receptors for a variety of ligands that are normally taken up by the cell, e.g. serum proteins, insulin, lipoproteins, etc. The receptors become concentrated in the pits either before or after association with their ligands. The process of C-c.v. formation from the plasma membrane is therefore known as receptor-mediated endocytosis... 

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