Potential vesicles

Nagy G, Matti U, Nehring RB et al (2002) Protein kinase C-dependent phosphorylation of synaptosome-associated protein of 25kDa at Serl87 potentiates vesicle recruitment. J Neu-rosci 22 9278-86... 

While vesicle deformation in AC fields concerns stationary shapes, DC pulses induce short-lived shape deformations. In different studies, the pulse duration has been typically varied from several microseconds to milliseconds, while studies on cells have investigated a much wider range of pulse durations-from tens of nanoseconds to milliseconds and even seconds [80], as discussed in other chapters of this book. Various pulse profiles, unipolar or bipolar, as well as trains of pulses have been also employed (e.g., [81, 82]). Because the application of both AC flelds and DC pulses creates a transmembrane potential, vesicle deformations of similar nature are to be expected in both cases. However, the working fleld strength for DC pulses is usually higher by several orders of magnitude. Thus, the degree of deformation can be different. 

Taylor, T.M., Gaysinsky, S., Davidson, P.M., Brace, B.D., Weiss, J., 2007. Characterization of antimicrobial-bearing liposomes by -potential, vesicle size, and encapsulation efficiency. Food Biophysics 2, 1—9. 

Two nucleation processes important to many people (including some surface scientists ) occur in the formation of gallstones in human bile and kidney stones in urine. Cholesterol crystallization in bile causes the formation of gallstones. Cryotransmission microscopy (Chapter VIII) studies of human bile reveal vesicles, micelles, and potential early crystallites indicating that the cholesterol crystallization in bile is not cooperative and the true nucleation time may be much shorter than that found by standard clinical analysis by light microscopy [75]. Kidney stones often form from crystals of calcium oxalates in urine. Inhibitors can prevent nucleation and influence the solid phase and intercrystallite interactions [76, 77]. Citrate, for example, is an important physiological inhibitor to the formation of calcium renal stones. Electrokinetic studies (see Section V-6) have shown the effect of various inhibitors on the surface potential and colloidal stability of micrometer-sized dispersions of calcium oxalate crystals formed in synthetic urine [78, 79]. 

Many complex systems have been spread on liquid interfaces for a variety of reasons. We begin this chapter with a discussion of the behavior of synthetic polymers at the liquid-air interface. Most of these systems are linear macromolecules however, rigid-rod polymers and more complex structures are of interest for potential optoelectronic applications. Biological macromolecules are spread at the liquid-vapor interface to fabricate sensors and other biomedical devices. In addition, the study of proteins at the air-water interface yields important information on enzymatic recognition, and membrane protein behavior. We touch on other biological systems, namely, phospholipids and cholesterol monolayers. These systems are so widely and routinely studied these days that they were also mentioned in some detail in Chapter IV. The closely related matter of bilayers and vesicles is also briefly addressed. 

Phospholipid molecules form bilayer films or membranes about 5 nm in thickness as illustrated in Fig. XV-10. Vesicles or liposomes are closed bilayer shells in the 100-1000-nm size range formed on sonication of bilayer forming amphiphiles. Vesicles find use as controlled release and delivery vehicles in cosmetic lotions, agrochemicals, and, potentially, drugs. The advances in cryoelec-tron microscopy (see Section VIII-2A) in recent years have aided their characterization [70-72]. Additional light and x-ray scattering measurements reveal bilayer thickness and phase transitions [70, 71]. Differential thermal analysis... 

Consider a phospholipid vesicle containing 10 mMNa ions. The vesicle is bathed in a solution that contains 52 mMNa ions, and the electrical potential difference across the vesicle membrane Ai/t = i/toutskie / inside = —30 mV. What is the electrochemical potential at 25°C for Na ions ... 

Functionalized polyelectrolytes are promising candidates for photoinduced ET reaction systems. In recent years, much attention has been focused on modifying the photophysical and photochemical processes by use of polyelectrolyte systems, because dramatic effects are often brought about by the interfacial electrostatic potential and/or the existence of microphase structures in such systems [10, 11], A characteristic feature of polymers as reaction media, in general, lies in the potential that they make a wider variety of molecular designs possible than the conventional organized molecular assemblies such as surfactant micelles and vesicles. From a practical point of view, polymer systems have a potential advantage in that polymers per se can form film and may be assembled into a variety of devices and systems with ease. 

Purinergic System. Figure 2 Schematic of sympathetic cotransmission. ATP and NA released from small granular vesicles (SGV) act on P2X and a-i receptors on smooth muscle, respectively. ATP acting on inotropic P2X receptors evokes excitatory junction potentials (EJPs), increase in intracellular calcium ([Ca2+]j) and fast contraction while occupation of metabotropic ar-adrenoceptors leads to production of inositol triphosphate (IP3), increase in [Ca2+]j and slow contraction. Neuropeptide Y (NPY) stored in large granular vesicles (LGV) acts after release both as a prejunctional inhibitory modulator of release of ATP and NA and as a postjunctional modulatory potentiator of the actions of ATP and NA. Soluble nucleotidases are released from nerve varicosities, and are also present as ectonucleotidases. (Reproduced from Burnstock G (2007) Neurotransmission, neuromodulation cotransmission. In Squire LR (ed) New encyclopaedia of neuroscience. Elsevier, The Netherlands (In Press), with permission from Elsevier). 

The surface potential can play an important role in the behavior of liposomes in vivo and in vitro (e.g.. Senior, 1987). In general, charged liposomes ai e more stable against aggregation and fusion than uncharged vesicles. However, physically stable neutral liposomes have been described (e.g.. Van Dalen et al., 1988). They are sufficiently stabilized by repulsive hydration forces, which counteract the attractive van der Waals forces. 

An alternative approach is the use of pH-sensitive fluorophores (Lichtenberg and Barenholz, lOSS). These probes are located at the lipid-water interface and their fluorescence behavior reflects the local surface pH, which is a function of the surface potential at the interface. This indirect approach allows the use of vesicles independent of their particle size. Recently, techniques to measure the C potential of Liposome dispersions on the basis of dynamic light scattering became commercially available (Muller et al., 1986). 

Mayer, L. D., Bally, M. B., Hope, M. J., and Cullis, P. R. (1985b). Uptake of antineoplastic agents into large unilamellar vesicles in response to a membrane potential, Biochim. Biophys. Acta. 816. 294-302. 

Historically, after the development of oligopeptide-based vesicles, several groups developed and characterized vesicles using polypeptide hybrid systems consisting of polypeptide and synthetic polymer blocks [17-19]. Soon thereafter, vesicles formed entirely from polypeptides, such as poly(L-lysine)-h-poly(L-leucine) and poly(L-lysine)-h-poly(L-glutamate), were developed [20, 21]. This review will focus on recent developments in the formation of vesicles composed of polypeptide hybrid or polypeptide systems, as well as the potential promise of these systems as effective dmg delivery vehicles. A specific example of a polypeptide-based vesicle is shown in Fig. 1, where the hydrophobic segment is a-helical and the hydrophilic segment is a random coil. 

We have proposed that vesicle aggregation is probably related to the disposition of pardaxin bound in the phosphatidylserine vesicle lipid bilayer (26). This conclusion is supported by the observation that phosphatidycholine vesicles are not induced to aggregate and that the pardaxin-induced phosphatidylserine vesicle aggregation is affected by charge polarization of the vesicle (26). This suggestion seems to be consistent also with the voltage dependence of fast "pore" activity of pardaxin, the channels which are open only at positive membrane potentials. 

To achieve their different effects NTs are not only released from different neurons to act on different receptors but their biochemistry is different. While the mechanism of their release may be similar (Chapter 4) their turnover varies. Most NTs are synthesised from precursors in the axon terminals, stored in vesicles and released by arriving action potentials. Some are subsequently broken down extracellularly, e.g. acetylcholine by cholinesterase, but many, like the amino acids, are taken back into the nerve where they are incorporated into biochemical pathways that may modify their structure initially but ultimately ensure a maintained NT level. Such processes are ideally suited to the fast transmission effected by the amino acids and acetylcholine in some cases (nicotinic), and complements the anatomical features of their neurons and the recepter mechanisms they activate. Further, to ensure the maintenance of function in vital pathways, glutamate and GABA are stored in very high concentrations (10 pmol/mg) just as ACh is at the neuromuscular junction. 

ATP certainly fulfils the criteria for a NT. It is mostly synthesised by mitochondrial oxidative phosphorylation using glucose taken up by the nerve terminal. Much of that ATP is, of course, required to help maintain Na+/K+ ATPase activity and the resting membrane potential as well as a Ca +ATPase, protein kinases and the vesicular binding and release of various NTs. But that leaves some for release as a NT. This has been shown in many peripheral tissues and organs with sympathetic and parasympathetic innervation as well as in brain slices, synaptosomes and from in vivo studies with microdialysis and the cortical cup. There is also evidence that in sympathetically innervated tissue some extracellular ATP originates from the activated postsynaptic cell. While most of the released ATP comes from vesicles containing other NTs, some... 

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