SBA Answers and Explanations
Vivian A. Elwell, Jonathan M. Fishman, Rajat Chowdhury in SBAs for the MRCS Part A, 2018
The resting membrane potential is dependent on the electrogenic sodium–potassium ATPase pump and the relative intracellular and extracellular concentrations of ions on each side of the nerve cell membrane, as well as their relative permeabilities across the membrane. This establishes both a concentration (chemical) gradient and an electrical gradient across the nerve cell membrane – an electrochemical gradient. The equilibrium potential for a given ion species depends on the ratio of the concentrations of the ion outside to that inside the cell (the Nernst potential or equation). The Goldman constant-field (or Goldman–Hodgkin–Katz) equation is a more general form of the Nernst equation which allows for different permeabilities. Resting nerve cell membranes are about 100 times more permeable to K+ ions than to Na+ ions.
Nutritional Ergogenic Aids: Introduction, Definitions and Regulatory Issues
Ira Wolinsky, Judy A. Driskell in Nutritional Ergogenic Aids, 2004
In these complexes the electrons carried by NADH (the reduced form of NAD) and FADH2 (the reduced form of FAD) from Complexes I and II are passed onto CoQ10, converting it from oxidized form to reduced form, which in turn passing the electrons to the cytochromes in Complex III while CoQ10 being oxidized again. The oxidized CoQ10 migrates in the membrane back to Complexes I and II to start the next “shuttle” movement. At the same time, protons are transported from the matrix side across the inner mito-chondrial membrane. This movement of protons creates an electrochemical gradient as the space outside of the inner membrane having more protons and a positive electrical charge. When the protons moving back into the matrix, driven by the gradient, energy is released which is used for the synthesis of ATP. The protons and electrons combine with oxygen to form water at the end of the electron transport chain, to complete the process.41 This aerobic energy transfer process will not work without an adequate level
DQAsomes as Mitochondria-Targeted Nanocarriers for Anti-Cancer Drugs
Mansoor M. Amiji in Nanotechnology for Cancer Therapy, 2006
One of the major roles of mitochondria in the metabolism of eukaryotic cells is the synthesis of Adenosine triphosphate (ATP) by oxidative phosphorylation via the respiratory chain. According to Mitchell’s chemiosmotic hypothesis, electrons from the hydrogens on Nicotine amide adenine dinucleotide (NADH) and Flavin adenine dinucleotide (FADH2) are carried along the respiratory chain at the mitochondrial inner membrane, thereby releasing energy that is used to pump protons across the inner membrane from the mitochondrial matrix into the intermembrane space. This process creates a transmembrane electrochemical gradient that includes contributions from both a membrane potential (negative inside) and a pH difference (acidic outside). The membrane potential of mitochondria in vitro is between 180 and 200 mV, the maximum a lipid bilayer can sustain while maintaining its integrity.66 Although this potential is reduced in living cells and organism to about 130–150 mV as a result of metabolic processes such as ATP synthesis and ion transport,67 it is by far the largest within cells.
Toxicological profile of lipid-based nanostructures: are they considered as completely safe nanocarriers?
Published in Critical Reviews in Toxicology, 2020
Asaad Azarnezhad, Hadi Samadian, Mehdi Jaymand, Mahsa Sobhani, Amirhossein Ahmadi
Transmission through the CM is either passive or active. In the passive transport, an ion or molecule moves in the direction of the electrochemical gradient or its concentration. This type of transfer is performed without the assistance of energy (ATP) and is occurred in two ways: simple and facilitated diffusion. However, the active transport uses energy to transfer ion or molecule against the concentration of electrochemical gradient (Murphy 2009; Singh et al. 2009). Polar or charged biomolecules that cannot pass through the hydrophobic plasma membrane are internalized by a form of active transport which is called endocytosis. Broadly speaking, the internalization routs can be classified as nonspecific pathways including: (i) pinocytosis (cellular drinking that involve small pinocytic vesicles (≈100 nm)) or (ii) macropinocytosis involving large vacuole formation (0.2–0.5 μm), as well as specific pathways such as (iii) clathrin- or caveolin-mediated endocytosis (the protein-coat-driven route) or (iv) phagocytosis of objects larger than 0.5 μm by specialized phagocytes (Tan et al. 2019).
Improving mitochondrial function in preclinical models of heart failure: therapeutic targets for future clinical therapies?
Published in Expert Opinion on Therapeutic Targets, 2023
Anna Gorący, Jakub Rosik, Joanna Szostak, Bartosz Szostak, Szymon Retfiński, Filip Machaj, Andrzej Pawlik
Heart failure is a complex clinical syndrome resulting from the unsuccessful compensation of symptoms of myocardial damage by several factors. Mitochondrial dysfunction is a process that occurs because of an attempt to adapt to the disruption of metabolic and energetic pathways occurring in the myocardium. This, in turn, leads to further dysfunction in cardiomyocyte processes. In the mitochondria, oxidation and reduction processes take place, generating the electrochemical gradients necessary for ATP synthesis. Mitochondrial energy metabolism is also a major source of ROS; therefore, it plays an important role in regulating oxidative stress. In addition to its key role in ATP synthesis and redox homeostasis, mitochondria are involved in numerous metabolic processes, in the oxidation of FA and amino acids, ion transport, and the synthesis of many other compounds that affect cardiomyocyte function [181,182].
Strobilurin fungicide kresoxim-methyl effects on a cancerous neural cell line: oxidant/antioxidant responses and in vitro migration
Published in Toxicology Mechanisms and Methods, 2018
Evangelia Flampouri, Dimitra Theodosi-Palimeri, Spyridon Kintzios
ROS generation elicits free-radical attacks on phospholipids, followed by loss of mitochondrial membrane potential with the opening of the permeability transition pore (PTP), resulting in the release of intermembrane proteins to the cytosol (Cai 2005). In our study, the higher two applied KM concentrations significantly induced mitochondrial membrane depolarization in N2a cells (Figure 2(C)). In the mitochondrial matrix space, the energy released from the electron movement through the respiratory complexes is used to pump H+ out of the matrix. This electrochemical gradient can be assessed by ΔΨm sensitive probes (Ohtake et al. 1997). Since KM disrupts electron flow, loss of the mitochondrial membrane potential could also be associated, besides ROS attacks on membrane phospholipids, with perturbation of the proton gradient across the inner mitochondrial membrane. Similar to our results, mitochondrial membrane depolarization after KM exposure has recently been reported in primary cortical neurons (Regueiro et al. 2015). Results on human skin keratinocytes (HaCaT) treated with trifloxystrobin, another cytochrome bc1 inhibitor of the strobilurin family, also reveal altered mitochondrial membrane potential (Jang et al. 2016), while H9c2 cardiomyocites treated with the strobilurin fungicide azoxystrobin, showed collapsed transmembrane mitochondrial potential with a dose-dependent increase in mitochondrial superoxide anion generation (Rodrigues et al. 2015).
Related Knowledge Centers
- Cellular Respiration
- Chemiosmosis
- Chloroplast
- Molecular Diffusion
- Photosynthesis
- Mitochondrion
- Electrochemical Potential
- Ion
- Membrane
- Adenosine Triphosphate