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Reconstituted Membrane Systems for Assaying Membrane Proteins in Controlled Lipid Environments
Published in Qiu-Xing Jiang, New Techniques for Studying Biomembranes, 2020
Another group of voltage-sensitive dyes are called ANNINE dyes. ANNINE-6plus is an example. These dyes have better sensitivity and thus an improved signal to noise ratio when compared to the hemocyanin dyes. They can measure even weak subthreshold synaptic potentials, which are generally difficult to do with conventional electrophysiology techniques.58 By now, a variety of voltage-sensitive dyes are available, differing in signal duration, intensity, signal to noise ratio, and cytotoxicity. A big disadvantage of these dyes is that most of them exhibit a small signal as a fluorescence change (0.1%) over a unit change (say 10 mV) in transmembrane potential, although some may reach 6% with a potential change of 100 mV. Because of such a limitation, low noise level in the detection system is a prerequisite for reliable determination of the relationship between fluorescence change and a change in transmembrane potential.
Voltage-Sensitive Dye and Intrinsic Signal Optical Imaging
Published in Yu Chen, Babak Kateb, Neurophotonics and Brain Mapping, 2017
Vassiliy Tsytsarev, Reha S. Erzurumlu
VSDi is based on voltage-sensitive fluorescence probes that are fluorescent chemicals that change their optical features in response to the changes of the membrane potential. The molecules of the voltage-sensitive dyes bind to the external neural surface and play the role of energy transducers that transform changes in the transmembrane voltage into the changes in light absorption or emitted photons (Fromherz et al., 2008). Photosensitive devices record these changes. The voltage across the neural membrane generates a strong electric field, which affects voltage-sensitive dye molecule fluorescence properties. Changes in the transmembrane potential are linearly related to the fluorescence of the voltage-sensitive dye molecule, which follow the transmembrane voltage. The amplitudes of the VSDi signals are linearly correlated with changes in the membrane potential; therefore, these dyes are called potentiometric dyes.
Optical Cardiovascular Imaging
Published in Robert J. Gropler, David K. Glover, Albert J. Sinusas, Heinrich Taegtmeyer, Cardiovascular Molecular Imaging, 2007
Crystal M. Ripplinger, Guy Salama, Igor R. Efimov
Voltage-dependent changes in fluorescence of dye molecules are a consequence of interactions of the electric field with the dye molecules resulting in intra-and extra-molecular rearrangements of the dye in the membrane. Voltage-sensitive dyes are classified into two groups (8), fast and slow dyes, based on their response times and presumed molecular mechanisms. Only the fast probes are used in cardiac electrophysiology, due to their ability to respond to voltage changes in a matter of microseconds (9). The precise mechanisms underlying the voltage-dependent spectroscopic properties of fast voltage-sensitive dyes are still not fully understood. The electrochromic theory (10) states that a dye will be voltage sensitive if (i) the photon-produced excitation of the chromophore is accompanied by a shift in electric charge and (ii) the vector of intramolecular charge movement is parallel with the electric field gradient. Therefore, if charge movement in a dye molecule occurs perpendicular to the cell membrane, the dye’s fluorescence will be sensitive to changes in transmembrane potential. An alternative theory is the solvatochromic theory (11) which contends that dye molecules experience a change in the polarity of the lipid environment during reorientation produced by the voltage gradient. This dependency causes the spectral voltage-dependence of the chromophore.
3D bioprinting for organ and organoid models and disease modeling
Published in Expert Opinion on Drug Discovery, 2023
Amanda C. Juraski, Sonali Sharma, Sydney Sparanese, Victor A. da Silva, Julie Wong, Zachary Laksman, Ryan Flannigan, Leili Rohani, Stephanie M. Willerth
A gold-standard read-out for functional assessment of 3D printed cardiac tissues following their response to drugs is high-speed high-resolution optical mapping [89]. Optical mapping is a widely used noninvasive assessment tool to visualize action potential and its wave propagation to study cardiac electrophysiology. Voltage-sensitive dyes (e.g. Di-4-ANEPPS) or Ca2+ sensitive dyes (e.g. X-Rhod, Fluo-4) are used to monitor transmembrane potential changes or Ca2+ transient propagation, respectively [90,91]. Measuring transient Ca2+ provides quantitative information about Ca2+ handling properties of the cardiac tissue, such as conduction velocity and signal intensity, which helps investigate the clinical phenotype of inherited heart diseases in vitro [7]. For example, it can be used to recapitulate hallmark features of catecholaminergic polymorphic ventricular tachycardia by showing ectopic Ca2+ propagation from patient-derived cardiac tissues with rapid electrical pacing or adrenergic stimulation [92].
Why do platelets express K+ channels?
Published in Platelets, 2021
Joy R Wright, Martyn P. Mahaut-Smith
Due to their fragile nature and small size, the number of direct patch clamp studies of the mammalian platelet remains limited (reviewed in [1]). Megakaryocytes are often used as a substitute for electrophysiological studies, and there is good evidence to suggest that the mature precursor cell is essentially a “giant” nucleated platelet [17,18]. Nevertheless, caution should be taken, particularly in terms of the detailed properties of channel activation, due to the substantial morphological rearrangements that take place during thrombopoiesis. While patch clamp is considered the “gold standard” when assessing ion channel properties, the challenge of applying this approach in the platelet means that much of the literature has assessed channel presence and contribution using less direct techniques. These include voltage-sensitive dyes, Rb+ flux measurements (since K+ channels are normally also permeable to Rb+, which can be measured using a radioactive isotope or a nonradioactive assay), proteomics and antibody-based approaches such as immunohistochemistry [3,4,9,14,19]. It is also worthwhile using a comparative approach as platelets and other blood cells are derived from a common stem cell within the marrow and studies of ion channels in other myeloid cells are substantially more advanced. While there are clear differences in channel complements between blood cell types (e.g. erythrocytes express KCa3.1 but not Kv1.3 [20,21]), there are major similarities, particularly regarding leukocyte K+ channels [20].
Strategies for targeting the cardiac sarcomere: avenues for novel drug discovery
Published in Expert Opinion on Drug Discovery, 2020
Joshua B. Holmes, Chang Yoon Doh, Ranganath Mamidi, Jiayang Li, Julian E. Stelzer
There are several available tools for studying cardiovascular physiology and pharmacodynamics in animal models. These include artificially perfused isolated hearts (e.g. Langendorff model), invasive pressure-volume (PV) hemodynamic analysis, ultrasound echocardiogram, and cardiac magnetic resonance (CMR) imaging. One advantage of perfused isolated heart models is the ability to easily manipulate perfusion parameters such as coronary flow rate/pressure, preload, and afterload while isolating the heart from the effects of animal stress and sympatho-adrenergic activation [105]. One can also easily study the electrical properties of the heart by direct surface electrical conductance recording, voltage-sensitive dye optical mapping, and surface electrode stimulation/pacing. These advantages make the perfused isolated heart an important tool in assessing the effects of pharmacologic intervention on cardiac electrophysiology and EC coupling.