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Neurotransmitters and Receptors, Ion Channels, G Proteins and Second Messengers
Published in Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal, Principles of Physiology for the Anaesthetist, 2020
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal
As the receptor and the ion channel are part of the same structure, the membrane response to acetylcholine is rapid; motor nerve endings are a good example of this. The nicotinic ion channel is permeable to both sodium and potassium ions; it may be as large as 6.5 Å in diameter. When the channel opens, the membrane approaches a ‘reversal potential’ between the potassium and sodium equilibrium potentials. The reversal potential is held constant until acetylcholine is metabolized by acetylcholinesterase, and the channel closes.
Membrane Properties of Peritoneal Macrophage
Published in Richard C. Niemtzow, Transmembrane Potentials and Characteristics of Immune and Tumor Cell, 2020
Such abrupt alterations in membrane potential imply a current-voltage relationship that is characteristically N-shaped with multiple crossings of the voltage axis (see Chapter 1, Figure 7). Usually such a relationship is due to a voltage-dependent conductance that increases as the membrane potential becomes more positive and which has a reversal potential at positive membrane potentials (see Chapter 1, Figure 6A and B for an example).
Computational Neuroscience and Compartmental Modeling
Published in Bahman Zohuri, Patrick J. McDaniel, Electrical Brain Stimulation for the Treatment of Neurological Disorders, 2019
Bahman Zohuri, Patrick J. McDaniel
The NMDAR is a specific type of ionotropic glutamate receptor. The NMDA receptor is so named because the agonist molecule N-methyl-D-aspartate (NMDA) binds selectively to it, and not to other glutamate receptors. Activation of NMDA receptors results in the opening of an ion channel that is nonselective to cations, with a combined reversal potential near 0 mV. While the opening and closing of the ion channel are primarily gated by ligand binding, the current flow through the ion channel is voltage dependent. Extracellular magnesium (Mg2+) and zinc (Zn2+) ions can bind to specific sites on the receptor, blocking the passage of other cations through the open ion channel. Depolarization of the cell dislodges and repels the Mg2+ and Zn2+ ions from the pore, thus allowing a voltage-dependent flow of sodium (Na+) and small amounts of calcium (Ca2+) ions into the cell and potassium (K+) out of the cell.
Computational modelling of mechano-electric feedback and its arrhythmogenic effects in human ventricular models
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2022
Yongjae Lee, Barış Cansız, Michael Kaliske
SACs are one of the physiological mechanisms behind MEF in cardiac tissue (Kohl et al. 1999; Hu and Sachs 1997). Since SACs were first demonstrated via experiments with amphibian ventricle (Lab 1978), there has been a considerable progress in research on MEF with developments of mathematical models for SACs. Sachs (1994) firstly attempted to incorporate SACs associated with sarcomere length as a measure of strain into the guinea-pig ventricular cell model (Noble 1992), whose results agreed well with the experimental observations. The effect of SACs observed in the experiments was reformulated by Sachs (1994) in terms of the fibre stretch, the maximum channel conductance and the reversal potential. Panfilov et al. (2005) have incorporated this mathematical model for SACs into an electromechanical model, where they found that the mechanical deformation results in automatic pacemaking activity via SACs. Moreover, mechanically induced arrhythmia was examined with recruitment of two types of SACs, cation-nonselective and potassium-selective channels by using a purely electrophysiological model (Trayanova et al. 2010) and by using a coupled electromechanical model (Jie et al. 2010). Lunze et al. (2010) added a term for open channel probability that depends on the myocardial strain to the model, which was incorporated into a 3 D human ventricular model within a human torso geometry and 12-lead electrocardiogram (ECG) was computed. Costabal et al. (2017) hypothesized that MEF may occur by additional deformations due to inertia effects and studied the alteration of wave dynamics via MEF using electromechanical models.
Loss of mGluR1-LTD following cocaine exposure accumulates Ca2+-permeable AMPA receptors and facilitates synaptic potentiation in the prefrontal cortex
Published in Journal of Neurogenetics, 2021
In LTD experiments, stable EPSCs were first obtained for 10 min as the baseline, followed by 10 min application of mGluR drugs to the bath, and EPSCs were then recorded for another 60 min. LTD was measured as the percentage of the averaged EPSCs between 50 and 60 min post drug application to the baseline EPSC. For Naspm (1-naphthylacetyl spermine trihydrochloride) sensitivity measurement, stable EPSCs were recorded for 10 min as the baseline, followed by 10–15 min application of the drug delivered to the bath to measure the reduction of EPSC. For the rectification measurement, EPSCs were recorded at −60 mV and +60 mV, respectively. Rectification index was calculated as the EPSC amplitude at +60 mV divided by that at −60 mV. EPSC reversal potential was assumed to be ∼0 mV for mPFC L5 neurons in our preparation. Cells were otherwise held at −60 mV during voltage-clamp experiments.
Interaction of low frequency external electric fields and pancreatic β-cell: a mathematical modeling approach to identify the influence of excitation parameters
Published in International Journal of Radiation Biology, 2018
Sajjad Farashi, Pezhman Sasanpour, Hashem Rafii-Tabar
In Equations (3) and (4), VhXand VmXdenote the Nernst or reversal potential for inactivation and activation functions, respectively. The conductivity of the voltage-sensitive channel is determined by the product of activation and inactivation functions and based on the structure of the channel the product of terms will be expressed by different expressions.