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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.
Elements of Bioelectricity
Published in Ashutosh Kumar Dubey, Amartya Mukhopadhyay, Bikramjit Basu, Interdisciplinary Engineering Sciences, 2020
Ashutosh Kumar Dubey, Amartya Mukhopadhyay, Bikramjit Basu
The energy, which is provided for the transport, is provided by ATP hydrolysis as well as thermodynamic free energy of various ions and solutes which is available in their concentration gradient. The ATP hydrolysis is utilized by pumps via primary active transport. In the secondary active transport, thermodynamic free energy available in the concentration gradient of solutes and ions is utilized for the transport by cotransporters and exchangers. Pumps, which utilize the energy provided by ATP hydrolysis, are called as ATPases. Most prominent ATPase is the Na–K pump, which extrudes three Na+ ions from a cell with a concurrent uptake of two K+ ions into the cell for hydrolysis of one molecule of ATP. This pump is generally called as electrogenic, because there is a net transfer of charge across the membrane. The Na–K pump is the only membrane protein that transfers Na+ ions through primary active transport.1,2,4
Applications in Biology
Published in Gabriel A. Wainer, Discrete-Event Modeling and Simulation, 2017
The chief function of the mitochondria is to create energy for cellular activity by the process of aerobic respiration. In this process, glucose is broken down in the cell’s cytoplasm, via the glycolysis process, to form pyruvic acid. In a series of reactions, part of which is called the Krebs cycle, the pyruvic acid reacts with water to produce carbon dioxide and hydrogen. Energy is released as the electrons flow from the coenzymes down the electron transport chain to the oxygen atoms. The enzyme ATPase, which is embedded in the inner membrane, adds a phosphate group to adenosine diphosphate (ADP) in the matrix to form ATP. Aerobic respiration is an ongoing process, and mitochondria can produce hundreds of thousands of ATP molecules per minute. ATP is transported to the cytoplasm, where it is used for virtually all energy-requiring reactions. As ATP is used, it is converted into ADP, which is returned by the cell to the mitochondrion and is used to build more ATP [19]. Specific enzymes control each of the different reactions, as shown in Figure 8.32.
Insights into the potential mechanism underlying liver dysfunction in male albino rat exposed to gasoline fumes
Published in Egyptian Journal of Basic and Applied Sciences, 2021
Folarin Owagboriaye, Sulaimon Aina, Rasheed Oladunjoye, Titilola Salisu, Adedamola Adenekan, Gabriel Dedeke
It has been reported that ATPases associated with membrane indicate alterations to the membrane under the condition of oxidative stress [51]. By hydrolysis, ATPases supply energy to metabolic processes, regulate membrane permeability and transportation of ions (including Na+, Ca2+ and K+) across the membrane at the expense of ATP [52]. In this study, gasoline fumes was observed to reduce the activities of membrane bound Ca2+-ATPase, Mg2+-ATPase, Na+/K+-ATPase and Total ATPase in the liver of the exposed rats. Na+/K+-ATPase is lipid dependent and has high affinity for SH group and Mg2+-ATPase activity is sensitive to lipid peroxidation [53]. Hence, we can attribute the reduction of these enzyme activities to the observed increased in lipid peroxidation by ROS in the liver of the exposed rats. It is also possible for some gasoline components in the tissue to have bonded with several SH-rich enzyme proteins and consequently inactivate them [34]. Reductions in the activities of these ion dependents ATPases could impair signal transduction due to a disturbance in ion homeostasis in the liver, an alteration in cellular metabolism, change cell membrane integrity and permeability as well as induce a rise in membrane fluidity and disturbances in vital functions [54]. In addition [53], noted that Na+/K+-ATPase inhibition could lead to a decrease in sodium efflux, which disrupts membrane permeability, a condition that leads to the leakage of Ca2+ ions into the cytoplasm. This will consequently decrease the activity of Ca2+-ATPase in the membrane, thereby potentiating irreversible cell destruction. This mechanism could also be a possibility in the liver of the gasoline fumes exposed rats in this study.
Glucosamine modulates membrane and cellular ionic homeostasis: studies on accelerated senescent and naturally aged rats
Published in Egyptian Journal of Basic and Applied Sciences, 2022
Komal Saraswat, Raushan Kumar, Syed Ibrahim Rizvi
The mammalian erythrocyte membrane provides a valuable model to investigate aging-related changes [6,7]. Erythrocyte membrane-bound transporters or pumps such as Ca2+ATPase (PMCA pump), Na+/K+-ATPase (NKA pump), and Na+/H+ exchanger (NHE) use the energy of ATP hydrolysis to move ions or small molecules across the membrane against a chemical concentration gradient or electric potential [8]. A close relationship has been established between the impairment in the activities of various membrane transporters and the development of pathologies [9].