Intracellular vesicles

The presently known mammalian AQP0-AQP12 have been localized in tissues involved in fluid transport as well as in nonfluid-transporting tissues (Table 1). Most AQPs are constitutively present in the plasma membrane, whereas some water channels can be triggered to shuttle between intracellular vesicles and the plasma membrane [2]. 

AQP6 is expressed in the intercalated cells of the kidney collecting duct. This channel is hardly permeable to water, but capable of transporting anions, including chloride, and is therefore thought to play a role in maintenance of body acid-base balance or in intracellular vesicle acidification. 

Intracellular vesicle that carries complexes of endocytic receptors with their ligand cargo internalized from the cell surface. 

During exocytosis, intracellular vesicles fuse with the plasmalemma. As a consequence, the vesicle components are incoiporated into the plasma membrane and the vesicle content is released into the extracellular space. We distinguish constitutive and regulated exocytosis. 

GLUT4 is a glucose transporter exclusively expressed in tissues with insulin-sensitive glucose uptake (heart, muscle, fat). Under basal conditions, GLUT4 is predominantly located in intracellular vesicles, and is... 

Vacuolar-type proton translocating ATPase is a heter-eomeric protein complex, which appears to translocate two protons across the vesicle membrane for each ATP molecule that is hydrolyzed, generating chemical (ApH) and electrical (A ) gradients. Although the ATPases present on different classes of intracellular vesicle have... 

Figure 13.9 represents the TEM image of LDH particles and their cellular internalization. As expected, LDH particles are internalized by endocytosis. Figure 13.9(A) shows the cellular uptake process of LDHs after 3h of treatment, and demonstrates a successive entry of LDH by endocytosis first the LDH particles were located around the cell membrane due to their positive charge ( ), then they migrate to the membrane ruffles which are considered as endocytic bodies ( ), finally the coated intracellular vesicles were formed as early endosomes ( ). Figure 13.9(B)...

Other systems like electroporation have no lipids that might help in membrane sealing or fusion for direct transfer of the nucleic acid across membranes they have to generate transient pores, a process where efficiency is usually directly correlated with membrane destruction and cytotoxicity. Alternatively, like for the majority of polymer-based polyplexes, cellular uptake proceeds by clathrin- or caveolin-dependent and related endocytic pathways [152-156]. The polyplexes end up inside endosomes, and the membrane disruption happens in intracellular vesicles. It is noteworthy that several observed uptake processes may not be functional in delivery of bioactive material. Subsequent intracellular obstacles may render a specific pathway into a dead end [151, 154, 156]. With time, endosomal vesicles become slightly acidic (pH 5-6) and finally fuse with and mature into lysosomes. Therefore, polyplexes have to escape into the cytosol to avoid the nucleic acid-degrading lysosomal environment, and to deliver the therapeutic nucleic acid to the active site. Either the carrier polymer or a conjugated endosomolytic domain has to mediate this process [157], which involves local lipid membrane perturbation. Such a lipid membrane interaction could be a toxic event if occurring at the cell surface or mitochondrial membrane. Thus, polymers that show an endosome-specific membrane activity are favorable. 

As outlined in previous sections, escape of polyplexes from endosomes to the cytosol can be a major bottleneck in delivery. Membrane-active polymer domains or other conjugated molecules can help to overcome this barrier (see Sect. 2.3), but they may trigger cytotoxicity when acting extracellularly or at the cell surface. Therefore membrane-crossing agents either have to be inherently specific for endo-somal compartments (for example by pH-specificity), or they have to be modified to be activated in endosomes. For example, the reducing stimulus of intracellular vesicles has been used to activate formulations containing less active disulfide precursors of LLO [163] or Mel [170]. 

Basal levels of Ca2+ in resting neutrophils are around 100 nM. Upon stimulation with soluble agonists such as fMet-Leu-Phe, PAF and LTB4, intracellular levels rise to about 1 pM within 20-30 s and then return to basal levels. Experiments in which neutrophils are suspended in media devoid of Ca2+ (and containing EGTA to chelate trace contaminants of this cation), show that although the initial rise in intracellular Ca2+ is unaffected, the elevation in concentration is not sustained when extracellular Ca2+ is absent. Thus, the initial rise in intracellular Ca2+ is due to mobilisation of intracellular stores Ca2+ influx is then activated in order to sustain these levels (Fig. 6.11). Addition of Ins 1,4,5-P3 to permeabilised neutrophils results in a rapid (within 2 s) rise in intracellular Ca2+, which then declines to basal levels, possibly as a result of the released Ca2+ returning to the intracellular stores. These intracellular vesicles must therefore have independent Ca2+ efflux and influx. 

LY294002 and wortmannin inhibit the enzyme PI-3 kinase required for the closure of pseudopodia to form intracellular vesicles (61,73-75,78,122). Compared to wortmannin, which is relatively unstable in aqueous media, the inhibitory effects of LY294002 are more specific, reversible (recovery after 10 minutes), and not light dependent. Therefore, LY294002 can be used for time-lapse experiments. Several studies have indicated that both substances have little or no effect on the other pathways described (75). However, both substances might block the uptake of Tfn as well (76). 

The release of intracellular constituents by fusion of an intracellular vesicle with the plasma membrane, thereby exposing the contents to the outer surface. 

Rabaptin 5 Membrane protein that regulates intracellular vesicle traffic (S9)... 

The adrenal medulla synthesizes two catecholamine hormones, adrenaline (epinephrine) and noradrenaline (norepinephrine) (Figure 1.8). The ultimate biosynthetic precursor of both is the amino acid tyrosine. Subsequent to their synthesis, these hormones are stored in intracellular vesicles, and are released via exocytosis upon stimulation of the producer cells by neurons of the sympathetic nervous system. The catecholamine hormones induce their characteristic biological effects by binding to one of two classes of receptors, the a- and )S-adrenergic receptors. These receptors respond differently (often oppositely) to the catecholamines. 

Amantidine and rimantidine belong to this class. Both are synthetic derivatives of the tricyclic amines and were noted by chance to have antiviral activity. Both agents destroy intracellular vesicles involved in the uptake of virus to host cells. They inhibit the myxoviruses, rubella, respiratory syncytial, and influenza A... 

Cyclic AMP is eventually eliminated by cAMP phosphodiesterase, and Gs turns itself off by hydrolysis of its bound GTP to GDP. When the epinephrine signal persists, j8-adrenergic receptor-specific protein kinase and arrestin 2 temporarily desensitize the receptor and cause it to move into intracellular vesicles. In some cases, arrestin also acts as a scaffold protein, bringing together protein components of a signaling pathway such as the MAPK cascade. 

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