Atherosclerosis
George Feuer, Felix A. de la Iglesia in Molecular Biochemistry of Human Disease, 2020
The vascular endothelium is permeable to a wide range of molecules. The permeability of the endothelium involves the presence of a pore system and the vesicular transport. Physiological studies on capillary transport revealed the existence of a two-pore system, one with small pores of approximately 9 μm in diameter and the other with large pores about 50 μm in diameter. Molecules up to 500,000 Da cross the endothelium by vesicular transport. The vesicular transport is bidirectional or emits invaginations on the luminal plasma membrane. LDL of about 22 μm in diameter can move across the normal endothelium in pinocytotic vesicles. This type of transport is unlikely for the larger chylomicrons and intact VLDL molecules.568 Albumin and fibrinogen cross the arterial endothelium, and there are focal and regional differences in the permeability to these macromolecules.
Structural Organization of the Liver
Robert G. Meeks, Steadman D. Harrison, Richard J. Bull in Hepatotoxicology, 2020
As mentioned above, proteins and lipoproteins are transported through the hepatocytes via membrane-bound vesicles and excreted into the blood. Vesicular transport is also involved in the endocytosis, intracellular transport, and exocytosis of a variety of other substances. Certain macromolecules are internalized specifically by receptor-medicated endocytosis, which differs from nonspecific fluid phase pinocytosis in that it involves binding of the ligand to be internalized to a specific receptor on the surface of the cell. Because endocytosis involves the formation of vesicles containing the ligand through pinching off from the plasma membrane, the ligand remains segregated from the cytoplasma by the surrounding vesicular membrane. Therefore, endocytosis differs from carrier-mediated transport systems, by catalizing the movement of small polar molecules and ions directly across the membrane barrier separating two aqueous compartment (Forgac, 1988).
Exocytosis of Nonclassical Neurotransmitters
Tian-Le Xu, Long-Jun Wu in Nonclassical Ion Channels in the Nervous System, 2021
Different from fast transmitters that form classical point-to-point transmission, dopamine was suggested to be released via a volume transmission mode, where neuromodulators diffuse to mediate effects in many cells over a large area or a longer distance (Agnati et al., 1995; Caille et al., 1996; Liu et al., 2018). Dopamine can also be released from soma and dendrites (Geffen et al., 1976). A large amount of morphological and functional evidence including immunohistochemistry, amperometry, and whole-cell voltage clamp support the belief that most of dopamine transmission is mediated by vesicular exocytosis (Caille et al., 1996; Kress et al., 2014; Staal et al., 2004; Uchigashima et al., 2016; Yung et al., 1995). The ablation of vesicular monoamine transporter type 2 (VMAT2) which is a major vesicular transporter for dopamine eliminates dopamine transmission (Fon et al., 1997). Here, we mainly focus on axonal dopamine release and related machinery involved in dopamine secretion.
Human ovarian granulosa cells use clathrin-mediated endocytosis for LDL uptake: immunocytochemical and electron microscopic study
Published in Ultrastructural Pathology, 2023
Aynur Abdulova, Merjem Purelku, Hakan Sahin, Gamze Tanrıverdi
Regarding the clathrin-mediated endocytic pathway, an important component is the clathrin protein. Clathrin-coated vesicles have a three-layered structure consisting of an outer region formed by clathrin proteins in the form of a cage, an intermediate region consisting of a lipid membrane, as well as internal adaptor proteins (APs).8 Along with clathrin, more than 60 other cytosolic proteins are involved in the formation of clathrin-coated endocytic vesicles.9 All these proteins assemble from the cytosol to the endocytic region in a highly ordered manner. The collected vesicles are transported to the target site by SNARE (N-ethylmaleimide-sensitive factor binding protein receptor) proteins. SNAREs manage the transfer of material to be transported during vesicular transport. In an animal cell, there are at least 20 different organelle-associated SNARE proteins, each attached to a specific membrane involved in the biosynthetic-secretion or endocytic pathway. These proteins function as transmembrane proteins and are referred to as vesicular SNAREs (v-SNAREs) with characteristic spiral domains.10
Toxicity of differently sized and charged silver nanoparticles to yeast Saccharomyces cerevisiae BY4741: a nano-biointeraction perspective
Published in Nanotoxicology, 2019
Kaja Kasemets, Sandra Käosaar, Heiki Vija, Umberto Fascio, Paride Mantecca
TEM observations revealed that differently from bPEI-coated AgNPs, citrate-coated AgNPs and exposure to AgNO3 caused an increase in the size of vacuoles (Figure 9). Similar ultrastructure changes upon exposure to AgNO3 and citrate-coated AgNPs could indicate the same mode of action of these Ag compounds. Indeed, the toxicity of 10 and 80 nm citrate-coated AgNPs was explainable by the shed Ag ions (Figure 4, Supporting Information Table S1). Vacuoles in the yeast cells are the main vesicular transport target organelles, resembling the lysosomes of the mammalian cells, having a large variety of macromolecules degrading capacity but also proteins and ions storage function (Li and Kane 2009). Increase in the size of the vacuoles is characteristic stress-response of yeast at the ionic stress conditions (Li and Kane 2009). TEM observation of 10nAg-Cit, 80nAg-Cit, and, AgNO3 exposed cells showed the presence of the dark/black electron dense area in the vacuoles (border of the vacuoles, see the white arrows in Figure 9). Silver has a high affinity for the sulfur compounds (Eckhardt et al. 2013) and the formation of silver-thiol-groups-containing proteins complexes may cause the proteins misfolding, subsequent non-functionality and degradation in the vacuoles. Moreover, silver has also high affinity to the phosphorus compounds and yeast vacuoles contain a lot of phosphorous (Li and Kane 2009). Hypothetically these black electron-dense areas in the vacuoles (Figure 9) may contain Ag-protein and Ag-phosphorous complexes.
Genetic identification of preoptic neurons that regulate body temperature in mice
Published in Temperature, 2022
Natalia L. S. Machado, Clifford B. Saper
However, the warm-responsive neurons in the POA are known to be intermixed with those that are cold-responsive [15–20]. To better understand the genetic identities of the neurons that are warm-responsive, Tan and colleagues used an elegant activity-dependent method to select neurons for mRNA sequencing. They found that a population of neurons clustered in the MnPO that are responsive to exposure to a warm ambient temperature express the peptides Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) and Brain-Derived Neurotrophic Factor (BDNF). Then, using calcium signaling in vivo, the authors demonstrated that MnPOPACAP/BDNF cells show a progressive increase in their activity during warm exposure. In line with these observations, the optogenetic activation of MnPOPACAP/BDNF neurons caused hypothermia by triggering heat dissipation and suppressing brown adipose tissue (BAT) thermogenesis. Tan and coworkers also investigated the brain circuitry by which MnPOPACAP/BDNF neurons regulate heat defense responses, and found that optogenetic activation of synaptic terminals innervating the DMH caused a decrease in the BAT temperature of about 1.2°C. Single-cell mRNA expression profiling demonstrated that many MnPOPACAP/BDNF neurons express GAD1 or GAD2 which led to early speculation that they were GABAergic [21]. However, later studies found that most of these neurons express Vglut2, but only one subset of these neurons co-expresses the vesicular transporter for GABA (Vgat), indicating that they are predominantly glutamatergic [22,23].
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