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Special Measurement Techniques
Published in Sujoy K. Guba, Bioengineering in Reproductive Medicine, 2020
With the modern accurate digital voltage measuring devices being available the procedure is quite straightforward. A constant sinusoidal AC current of known magnitude I is generated by means of an electronic oscillator circuit and passed between the electrodes which are placed in contact with the body tissue. The potential difference V is measured between the electrodes with a digital voltmeter. Impedance Z is obtained by dividing V by the current magnitude I. This procedure is known as the “two electrode technique” (Figure 2.9a). The method is simple and useful in certain applications for instance the monitoring of the motility of the oviduct but has limitations. At the electrodes there is inevitably some polarization effect and the polarization impedance, the magnitude of which is not known, being in series with the tissue impedance figures in the net impedance Z derived by the two electrode technique. Polarization impedance may change thereby introducing uncertainties in the interpretation of any impedance shifts observed.
The Nist Power Reference Source
Published in Marvin C. Ziskin, Peter A. Lewin, Ultrasonic Exposimetry, 2020
Specificity Have the obvious side effects inherent to the basic functions of the EUT been effectively suppressed?Since all power-measuring instruments derive measured data from a long chain of inferences (e.g., voltage → resistance → temperature → heat → power; voltage × current → power for a balanced calorimeter), sources of systematic error are abundant. Each basic function must be considered in the design of an instrument, and should be understood and checked by the end user.Have all assumptions necessary to EUT operation under typical conditions been sufficiently proven?Under practical lab conditions, even the obvious cannot always be trusted. Anything which must be assumed (e.g., that a voltmeter is as stable when connected as when isolated) should be checked under conditions as close as possible to actual working conditions (e.g., with voltmeter cable shield connected to voltage source, shielded conductor isolated).
The cardiac myocyte: excitation and contraction
Published in Neil Herring, David J. Paterson, Levick's Introduction to Cardiovascular Physiology, 2018
Neil Herring, David J. Paterson
A microelectrode is a glass tube that has been heated, drawn out to a very fine point, filled with a conducting solution, and connected to an amplifier and voltmeter. The other lead of the voltmeter is connected to an extracellular electrode. The intracellular potential of the resting cardiac myocyte is −80 to −90 mV, that is, 80–90 mV lower than the extracellular fluid. In atrial and ventricular cells, the resting potential is stable (Figure 3.4), whereas in pacemaker cells and many conduction fibres (Purkinje fibres), it is unstable and drifts towards zero with time, a feature discussed in Chapter 4.
Impact of electrical stimulation on the growth of mycelium of lignosus rhinocerus (cooke) ryvarden
Published in Electromagnetic Biology and Medicine, 2020
Nor Azreen Mohd Jamil, Chandima Gomes, Zainal Kadir, Ashen Gomes
•Injection of direct current: The electrode at one side of Petri dish was connected to the positive terminal of the d.c. supply through a copper cable whereas the electrode on the other side of the Petri dish was connected to the negative terminal of the power supply. A voltmeter and an ammeter were connected to the circuit to observe the voltage and current readings. Control group mycelium in the Petri dish with electrode was left under the same environmental conditions without being connected to the power supply.
Correlation of the in vitro biotransformation of H3B-6527 in dog and human hepatocytes with the in vivo metabolic profile of 14C-H3B-6527 in a dog mass balance study
Published in Xenobiotica, 2020
F. Colombo, S. Smith, G. W. Lai, D. Nix, P. G. Smith, J. Schindler, N. Rioux
Evaluation of H3B-6527 (2, 10 and 20 μM) as a potential substrate of P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP) was conducted in Madin Darby Canine Kidney (MDCKII) cells overexpressing multi-drug resistance protein 1 (MDR1) or BCRP and in control MDCKII (nontransfected) cells (QPS, LLC via The Netherlands Cancer Institute). 24-Well Transwell® plates (Corning, Oneonta, NY) were used to grow cell monolayers for the permeability studies. Prior to experiment initiation, monolayer integrity was assessed by transepithelial electrical resistance (TEER) measurements using Millicell ERS-2 (EMD Millipore, Billerica, MA). The volt meter probe was placed into both basolateral and apical sides of the transwell simultaneously until resistance was measured and recorded. All transwells were tested and only wells that passed the acceptance criterion (TEER ≥ 200 Ω) were used in experiments. In addition, potential effects of up to 20 μM H3B-6527 on cell monolayer integrity was assessed by co-incubation with lucifer yellow for 90 min. Bidirectional permeability, apical-to-basolateral (A-to-B) and basolateral-to-apical (B-to-A), was assessed over time to characterize both permeability rate as well as efflux potential. For the transport assay, aliquots of fresh efflux buffer (Dulbecco’s Modified Eagle Medium/HEPES buffer, pH 7.4) containing H3B-6527 or a probe substrate in combination with control inhibitor or solvent, were added to the donor compartment, and efflux buffer were added to the receiver compartment. Plates were incubated on a 90 rpm orbital shaking apparatus in a 37 °C, 5% CO2 incubator; aliquots of donor and receiver samples were taken at 5 and 90 min, and added to one volume of organic solvent. The concentrations of H3B-6527 and probe substrate were determined by LC–MS/MS, using their corresponding deuterated analogs as IS. The apparent permeability coefficient (Papp) was calculated and the efflux ratios [Papp(B-to-A) over Papp(A-to-B)] were determined. As controls, the transport of digoxin (5 μM, a P-gp substrate) and cimetidine (3 μM, a BCRP substrate) was also measured in the absence or presence of GF120918/elacridar (2 μM, a P-gp inhibitor) or Ko143 (1 μM, a BCRP inhibitor), respectively (FDA, 2019; Takenaka et al., 2007).