The Cell Membrane in the Steady State
Nassir H. Sabah in Neuromuscular Fundamentals, 2020
Typically, a cubic micron of cytoplasm contains roughly: 1010 water molecules, 108 ions, 107 small molecules such as amino acids and nucleotides (Section 6.3.1), and 105 protein molecules. The ion species in the intracellular and extracellular media include Na+, K+, Cl–, H+, Ca2+, Mg2+, HCO3–, amino acids, proteins, and molecules with negatively charged phosphate groups (PO42–). Of these ion species, Na+, K+ and Cl– have relatively high concentrations, so they are the only ions usually considered in the discussion of the resting membrane voltage. Generally, the intracellular medium contains an excess concentration of negative charge, which makes the inside of the neuron at a negative voltage with respect to the outside. Many of the negatively charged, relatively large molecules, such as proteins, amino acids, and energy-rich phosphates cannot diffuse outside the cell and constitute the indiffusible anions A– considered in the Gibbs–Donnan Equilibrium (Section 1.5.4).
The heart
Laurie K. McCorry, Martin M. Zdanowicz, Cynthia Y. Gonnella in Essentials of Human Physiology and Pathophysiology for Pharmacy and Allied Health, 2019
The mechanism of these effects involves the increased permeability to potassium. The enhanced efflux of K+ ions has two effects on the action potential of the SA node. First, the cells become hyperpolarized so that the membrane potential is farther away from threshold (from a normal resting potential of −55 mV down toward −65 mV), and a greater depolarization is now needed to reach threshold and generate an action potential. Second, the rate of depolarization during the pacemaker potential is reduced. The outward movement of positively charged K+ ions opposes the depolarizing effect of the Na+ ion and Ca++ ion influx. In this way, action potentials are developed more slowly and fewer heartbeats are generated per minute (see Figure 7.6).
Positions in neurosurgery
Hemanshu Prabhakar, Charu Mahajan, Indu Kapoor in Essentials of Geriatric Neuroanesthesia, 2019
ION usually develops bilaterally and is associated with anesthetic duration greater than 6 hours, blood loss (more than 1000 mL), and blood transfusion (20). ION is also associated with other conditions, including diabetes, hypertension, smoking, atherosclerosis, anemia, ulcerative colitis, preexisting renal disease, sex, and obesity (19,21). The pathophysiology of ION is multifactorial and poorly understood, as it was shown not to be related to direct compression on the optic globe or any other specific prone position-related factor. ION has been reported to occur in patients who were placed on different frames and tables (Wilson frame, Jackson table, etc.) and with various head-supporting devises (Mayfield pinning, foam and gel pad), and independently whether or not regular eye check was documented during the surgery.
Comparative HPLC-MS/MS-based pharmacokinetic studies of multiple diterpenoid alkaloids following the administration of Zhenwu Tang and Radix Aconiti Lateralis Praeparata extracts to rats
Published in Xenobiotica, 2021
Yanhao Liu, Hua Sun, Chao Li, Zhicheng Pu, Zijing Wu, Maodi Xu, Xianghong Li, Yuanxiang Zhang, Hongjin Li, Jian Dong, Runlei Bi, Haitang Xie, Dahu Liang
To identify optimal MS conditions, six analytes, and appropriate internal standard (IS) compounds were prepared at defined concentrations that were injected into the mass spectrometer using electrospray ionisation (ESI) and MRM scanning mode. Peak ion intensity values in negative and positive ion modes were compared and were found to be more stable in positive ion mode. Optimised MS parameters used for this study are compiled in Table 1. Initially, two eluents (Methanol/water and acetonitrile/water) were evaluated as a mobile phase. The acetonitrile/water mobile phase system was found to yield higher S/N ratios and better separation. After testing different buffers and acid–base solutions in combination with this mobile phase system, higher responses, and better peak shape were observed, followed by adding the ammonium acetate and formic acid to the mobile phase. Column temperature, eluent flow rate, and volume of injection were optimised.
Utility of in vitro and in vivo systems for studying the permeability of capsaicin and nonivamide through different intestinal regions
Published in Xenobiotica, 2018
Lian Duan, Huaidong Peng, Guangcan Li, Ruolun Wang, Yanfang Chen
The in vitro and in vivo capsaicin concentrations were determined using an LC-MS/MS system (Agilent 6460 Triple Quadrupole LC/MS, Santa Clara, CA). The optimization conditions for LC-MS/MS were in accordance with the method established in a previously published article (Duan et al., 2013a). The LC-MS/MS system is simple, accurate, reliable and time-saving for determining trace amount of capsaicin in plasma. Capsaicin was chromatographed by injecting 2 μl of the sample into an Agilent SB-C18 column (1.8 μm, 2.1 mm × 50 mm). The mobile phase of 0.1% acetonitrile–formic acid (70–30, v/v) was run at a flow rate of 0.2 ml/min with an oven temperature of 30 °C. The ion source was an electrospray ionization interface in the positive mode. The drying gas temperature was maintained at 300 °C at a flow rate of 10 l/min with an ion spray voltage of 3.5 kV. The multiple reaction monitoring modes was used for the quantitative analyses. The precursor/product ion transitions were monitored at m/z 306 → 137 (+Ion mode) for capsaicin and m/z 293.4 → 137 (+Ion mode) for nonivamide. Verapamil was used as the internal standard at m/z455→165, at a collision energy of 22 eV. The dwell time for each transition was 200 ms. The retention time of capsaicin was 0.65 min, while the run time was 2 min for each sample.
Effect of the flame retardant tris (1,3-dichloro-2-propyl) phosphate (TDCPP) on Na+-K+-ATPase and Cl− transport in HeLa cells
Published in Toxicology Mechanisms and Methods, 2018
Simona Latronico, Maria Elena Giordano, Emanuela Urso, Maria Giulia Lionetto, Trifone Schettino
This work was addressed to investigate the effect of TDCPP on some membrane transport mechanisms involved in the ion cellular homeostasis fundamental for cell viability, such as the Na+-K+-ATPase pump and Cl− transport. The study was carried out on HeLa cells, a widely used in vitro model for toxicity testing. Intracellular ion homeostasis is fundamental for cell functions and the cell strongly needs to maintain a normal ionic balance to remain healthy and viable. Perturbations of the normal cytoplasmic ionic environment are associated with alteration of the cell cycle and cell death. Na+, K+, and Cl− are the main monovalent ions involved in the intracellular ion homeostasis. Perturbation of the concentration of these ions, such as decrease in the intracellular K+ and Cl− concentrations are associated to cell death (Wang et al. 2013).
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- Zwitterion
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