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Synapses
Published in Nassir H. Sabah, Neuromuscular Fundamentals, 2020
Small-molecule neurotransmitters, or simply neurotransmitters, are synthesized mainly in axon terminals and are actively packaged into small electron-lucent vesicles, about 40 nm in diameter, by transporters driven by a H+ electrochemical potential gradient. This gradient is established by a vacuolar-type H+-ATPase (V-ATPase) which uses the energy from ATP hydrolysis to pump H+ (protons) into vesicles. This results in a lower pH inside the vesicle and in a positive voltage of tens of millivolts or more with respect to the cytoplasm. The resulting electrochemical potential gradient for H+ is used to accumulate various substances inside the vesicle. The vesicles are released into the synaptic cleft at active zones through exocytosis (Section 1.1.3) mediated by the inflow of Ca2+ resulting from depolarization of the presynaptic terminal, as in the NMJ. However, there is evidence that in some cases neurotransmitters may be released by exocytosis from the axoplasm directly into the synaptic cleft. Vesicles may be round or flat in shape. It is believed that the former are found in excitatory synapses, whereas the latter are found in inhibitory synapses.
Measurement of lysosomal ion homeostasis by fluorescence microscopy
Published in Raquel Seruca, Jasjit S. Suri, João M. Sanches, Fluorescence Imaging and Biological Quantification, 2017
Benjamin König, Lisa von Kleist, Tobias Stauber
Lysosomes are the final compartments of the animal cell’s degradative endocytic and autophagic pathways. By degrading various molecules delivered to these organelles and providing the products as metabolites for new anabolic pathways, and by their additional function as signaling platform, lysosomes play a pivotal role in general cellular homeostasis [1,2]. The establishment and maintenance of various ion gradients between the interior of these compartments and the cytosol is crucial to facilitate the various physiological processes of lysosomes, and dysregulation of their ion homeostasis is involved in numerous diseases. A plethora of ion transport proteins ensures that the luminal concentrations of the different ions fit the needs of this organelle (Figure 14.1). The vacuolar-type ATPase (V-ATPase) provides for the acidic luminal pH (≤5) by pumping protons (H+) under the consumption of energy [3]. The low pH is important for the activity of lysosomal enzymes and for various membrane trafficking steps. Moreover, the pH gradient is used to drive secondary transport of metabolites and other ions against their electrochemical gradient by symporters and antiporters. The electrogenic proton pumping requires a parallel electrical shunt to prevent a rapid build up of an inside-positive potential that would inhibit further pumping by the V-ATPase. This could be the influx of anions such as chloride (Cl−) and/or efflux of cations such as sodium (Na+) or potassium (K+) [4–6]. Besides their potential role in supporting the acidification, these ions may play further roles in lysosomal physiology [7,8]. Another ion that has gained much attention for its importance in lysosomal function is calcium (Ca2+), whose luminal concentration may be up to 10,000-fold higher inside these organelles than in the cytosol. Its release is involved in signaling events and it can trigger the fusion of docked organelles with the plasma membrane and with other compartments [9,10]. Ca2+ release channels have been identified, whereas its uptake mechanism has remained enigmatic. In addition to the above-mentioned ions, many further inorganic ions—such as zinc (Zn2+), iron, phosphate, magnesium, and copper—can be found in lysosomes and lysosomes play an important role in their cellular homeostasis.
Microstructured titanium functionalized by naringin inserted multilayers for promoting osteogenesis and inhibiting osteoclastogenesis
Published in Journal of Biomaterials Science, Polymer Edition, 2021
Ke Shen, Xiaojing Zhang, Qiang Tang, Xingtang Fang, Chunlei Zhang, Zhaojing Zhu, Yanhua Hou, Min Lai
In order to better prove the inhibitory effect of LBL (NA) coated-Ti substrates on osteoclast formation, osteoclastic genes were measured using qRT-PCR after 7 days of culture and these results are shown in Figure 7. Cathepsin K (CTSK) encodes a member of the cysteine protease cathepsin family, which is highly expressed in osteoclasts and is involved in the degradation of collagen and other bone matrix proteins [42]. Nuclear factor of activated T cells (NFAT) is mainly expressed in immune cells and plays a key role in immune response [43]. Overexpression of TRAP is one of the main causes of osteoporosis and it is abundant in osteoclasts [41]. V-ATPase (VATP) is a specific site in the plasma membrane that is involved in the reabsorption of osteoclast attachment sites [44]. As can be seen from the Figure 7, the expression of these osteoclastic genes on LBL (NA) coated-Ti substrate decreased compared to Ti substrates. Osteoclastic genes on LBL coated-Ti substrates also decreased compared with Micro-Ti substrates to a certain extent. These results indicate that LBL (NA) coated-Ti substrates can inhibit osteoclast generation, which was inseparable from the role of NA. NA may abrogate osteoclastogenesis and bone resorption via the inhibition of RANKL-induced NF-κB and ERK activation [39].
Exenatide promotes the autophagic function in the diabetic hippocampus: a review
Published in Egyptian Journal of Basic and Applied Sciences, 2022
Eman Mohammed Elsaeed, Ahmed Gamal Abdelghafour Hamad, Omnia S. Erfan, Mona A. El-Shahat, Fathy Abd Elghany Ebrahim
Lysosomes are the main organelles regulating all the steps following autophagosome formation. They are capable of breaking down any biological material, as they contain acid hydrolases. Their integrity is primarily influenced by two factors: the soluble acid hydrolases and the lysosomal membrane proteins. A vacuolar ATPase maintains an acidic (pH ≤5) milieu by pumping protons into the lysosomal lumen, making the acid hydrolases able to work. The lysosomal membrane proteins such as lysosome-associated membrane protein (LAMP-1 & LAMP-2) act to protect the cytoplasm from the action of the acid hydrolases and regulate the fusion of the lysosomes with other organelles, including the autophagosomes [15].