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X-Nuclei MRI and Energy Metabolism
Published in Guillaume Madelin, X-Nuclei Magnetic Resonance Imaging, 2022
Ions such as sodium Na+, potassium K+, calcium ion Ca2+, chlorine Cl- (or chloride), hydrogen (proton) H+, magnesium Mg2+, phosphates ([PO4]3-, [HPO4]2-, [H2PO4]-) and bicarbonate HCO-3 play a fundamental role in many metabolic processes in the body. They are often also called electrolytes, and they are present in bodily fluids, and in both intracellular and extracellular spaces with different concentrations. These different ionic concentrations across the cell membrane create an electrochemical gradient. This gradient of electrochemical potential, for an ion that can move across a membrane, consists of two parts: (1) the chemical gradient, which is the difference in ion concentration across a membrane; and (2) the electrical gradient, which is difference in charge across a membrane, and which generate a membrane potential [1–5, 10–12, 30–32].
Electrophysiology
Published in Jay L. Nadeau, Introduction to Experimental Biophysics, 2017
Jay L. Nadeau, Christian A. Lindensmith, Thomas Knöpfel
Electrophysiology is a technique for measuring currents through membranes. Because lipid membranes are impermeable to charged species, currents cannot result from simple diffusion but instead require the presence of ion channel proteins in the membrane. Ion channels are pore-forming proteins that allow a flow of ions in the direction established by the cell’s electrochemical gradient. They usually display selectivity, allowing only one type of ion to pass, although nonselective ion channels also exist that pass either all anions or all cations. Ion channels are present in a wide variety of biological processes that cause rapid changes in cells: transport of nutrients, muscle contraction, the release of insulin in pancreas, and action potentials in the neurons of the nervous system and the cardiomyocytes of the heart. Cells that fire action potentials are called excitable cells.
Physical properties of the body fluids and the cell membrane
Published in Ronald L. Fournier, Basic Transport Phenomena in Biomedical Engineering, 2017
In general, the driving force for the passive transport of these solutes is due to the combined effect of their concentration gradient and the electric potential difference that exists across the membrane. Neutral molecules diffuse from regions of high concentration to regions of low concentration. However, if the molecule carries an electrical charge, then both the concentration gradient and the electric potential difference, or voltage gradient, across the cell membrane will affect the transport of the molecule. The electrochemical gradient is the term used to describe the combined effect of charge and solute concentration on the transport of a molecule. The voltage gradient for a cell membrane is such that the inside of the cell membrane is negative in comparison to the outside. This membrane potential (VM) for cells at rest is about −90 mV, which means that the potential inside the cell is 90 mV lower than the potential outside the cell.
Electrochemical evaluation of ion substituted-hydroxyapatite on HeLa cells plasma membrane potential
Published in Cogent Engineering, 2019
Bernard Owusu Asimeng, Elvis Kwason Tiburu, Elsie Effah Kaufmann, Lily Paemka, Claude Fiifi Hayford, Samuel Essien-Baidoo, Obed Korshie Dzikunu, Prince Atsu Anani
It is reported that disrupting the plasma membrane potential of cancer cells may trigger apoptosis (Zhang, Chen, Gueydan, & Han, 2017). Generally, cell plasma membranes generate potential (membrane potential) because of the imbalance of charges between the intracellular and extracellular environment. This arises from the presence of different ion channels which allow distinct ions such as Na+, K+, Ca2+ and Cl− access through the voltage-gates of the ion channels based on their specific size. Because of the difference in the number of ions within the cytoplasm and the extracellular medium, a voltage difference (electrochemical gradient) is always evolving. A normal cell tries to balance the ion concentration across the plasma membrane to achieve a resting potential through polarization. At resting potential, the cytoplasm becomes more negative. That is, more Na+ are sent outside and K+ are kept inside the cytoplasm (polarization). Typically, normal cells generate stimuli through polarization, for example, during muscle contraction (Lodish, Berk Arnold, Lawrence, & Baltimore David, 2000). On the contrary, cancer cells generate stimuli through plasma membrane depolarization (more Na+ are taken up by the cell and the cytoplasm becomes less negative). Depolarization generates strong stimuli that communicate faster, causing rapid proliferation (Yang & Brackenbury, 2013).