Voltage Dependence and Characterization of Ceramic Capacitors Under Electrical Stress

1. Calcium channel currents were measured with the whole-cell patch clamp technique in cultured, identified mouse motoneurons. Three components of current were operationally defined on the basis of voltage dependence, kinetics, and pharmacology. 2. Test potentials to -50 mV or greater (10 mM external Ca2+) elicited a low-voltage activated T-type current that was transient (decaying to baseline in less than 200 ms) and had a relatively slow time to peak (20-50 ms). A 1-s prepulse to -45 mV produced approximately half-maximal inactivation of this T current. 3. Two high-voltage activated (HVA) components of current (1 transient and 1 sustained) were activated by test potentials to -20 mV or greater (10 mM external Ca2+). A 1-s prepulse to -35 mV produced approximately half-maximal inactivation of the transient component without affecting the sustained component. 4. When Ba2+ was substituted for Ca2+ as the charge carrier, activation of the HVA components was shifted in the hyperpolarizing direction, and the relative amplitude of the transient HVA component was reduced. 5. Amiloride (1-2 mM) caused a reversible, partial block of the T current without affecting the HVA components. 6. The dihydropyridine agonist isopropyl 4-(2,1,3-benzoxadiazol-4-yl)-1,4-dihydro-2,6-dimethyl-5-nitro-3- pyridine-carboxylate [(+)-SDZ 202-791, 100 nM-1 microM)] shifted the activation of the sustained component of HVA current to more negative potentials and increased its maximal amplitude. Additionally, (+)-SDZ 202-791 caused the appearance of a slowed component of tail current.(ABSTRACT TRUNCATED AT 250 WORDS)

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LRRC8A homohexameric channels poorly recapitulate VRAC regulation and pharmacology

AJP Cell Physiology ◽

10.1152/ajpcell.00454.2020 ◽

2020 ◽

Author(s):

Toshiki Yamada ◽

Eric E. Figueroa ◽

Jerod S. Denton ◽

Kevin Strange

Keyword(s):

Electron Microscopy ◽

Voltage Dependence ◽

Function Analysis ◽

Cell Swelling ◽

Independent Manner ◽

Cryo Electron Microscopy ◽

Homologous Position ◽

Pore Properties ◽

Hct116 Cells

Swelling-activated VRACs are heterohexameric channels comprising LRRC8A and at least one other LRRC8 paralog. Cryo-electron microscopy (EM) structures of non-native LRRC8A and LRRC8D homohexamers have been described. We demonstrate here that LRRC8A homohexamers poorly recapitulate VRAC functional properties. Unlike VRACs, LRRC8A channels heterologously expressed in Lrr8c-/- HCT116 cells are poorly activated by low intracellular ionic strength (µ) and insensitive to cell swelling with normal µ. Combining low µ with swelling modestly activates LRRC8A allowing characterization of pore properties. VRACs are strongly inhibited by 10 mM DCPIB in a voltage-independent manner. In contrast, DCPIB block of LRRC8A is weak and voltage sensitive. Cryo-EM structures indicate that DCPIB block is dependent on arginine 103. Consistent with this, LRRC8A R103F mutants are insensitive to DCPIB. However, a LRRC8 chimeric channel in which R103 is replaced by a leucine at the homologous position is inhibited ~90% by 10 mM DCPIB in a voltage-independent manner. Coexpression of LRRC8A and LRRC8C gives rise to channels with DCPIB sensitivity that is strongly µ-dependent. At normal intracellular µ, LRRC8A+LRRC8C heterohexamers exhibit strong, voltage-independent DCPIB block that is insensitive to R103F. DCPIB inhibition is greatly reduced and exhibits voltage dependence with low intracellular µ. The R103F mutation has no effect on maximal DCPIB inhibition but eliminates voltage-dependence under low µ conditions. Our findings demonstrate that the LRRC8A cryo-EM structure and the use of heterologously expressed LRRC8 heterohexameric channels pose significant limitations for VRAC mutagenesis-based structure-function analysis. Native VRAC function is most closely mimicked by chimeric LRRC8 homohexameric channels.

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Characterization of Electrical Stress of Natural Ester Under Impulse Empirical Analysis

2018 IEEE 7th International Conference on Power and Energy (PECon) ◽

10.1109/pecon.2018.8684169 ◽

2018 ◽

Author(s):

Muhammad Ameerul Ikmal Ahmad Taufek ◽

Nur Darina Ahmad ◽

Siti Solehah Md Ramli ◽

Nurul Huda Ishak ◽

Mohd Taufiq Ishak ◽

...

Keyword(s):

Empirical Analysis ◽

Electrical Stress ◽

Natural Ester

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Calcium Current Activated by Depletion of Calcium Stores in Xenopus Oocytes

The Journal of General Physiology ◽

10.1085/jgp.109.6.703 ◽

1997 ◽

Vol 109 (6) ◽

pp. 703-715 ◽

Cited By ~ 51

Author(s):

Yong Yao ◽

Roger Y. Tsien

Keyword(s):

Xenopus Oocytes ◽

Voltage Dependence ◽

Calcium Stores ◽

Kinase C ◽

Electrode Voltage ◽

Activation Mechanisms ◽

Electrophysiological Characterization ◽

Inwardly Rectifying ◽

A Current

Ca2+ currents activated by depletion of Ca2+ stores in Xenopus oocytes were studied with a two-electrode voltage clamp. Buffering of cytosolic Ca2+ with EGTA and MeBAPTA abolished ICl(Ca) and unmasked a current in oocytes that was activated by InsP3 or ionomycin in minutes and by thapsigargin or the chelators themselves over hours. At −60 mV in 10 mM extracellular CaCl2, the current was typically around −90 or −160 nA in oocytes loaded with EGTA or MeBAPTA, respectively. This current was judged to be a Ca2+-selective current for the following reasons: (a) it was inwardly rectifying and reversed at membrane potentials usually more positive than +40 mV; (b) it was dependent on extracellular [CaCl2] with Km = 11.5 mM; (c) it was highly selective for Ca2+ against monovalent cations Na+ and K+, because replacing Na+ and K+ by N-methyl-d-glucammonium did not reduce the amplitude or voltage dependence of the current significantly; and (d) Ca2+, Sr2+, and Ba2+ currents had similar instantaneous conductances, but Sr2+ and Ba2+ currents appeared to inactivate more strongly than Ca2+. This Ca2+ current was blocked by metal ions with the following potency sequence: Mg2+ << Ni2+ ≈ Co2+ ≈ Mn2+ < Cd2+ << Zn2+ << La3+. It was also inhibited by niflumic acid, which is commonly used to block ICl(Ca). PMA partially inhibited the Ca2+ current, and this effect was mostly abolished by calphostin C, indicating that the Ca2+ current is sensitive to protein kinase C. These results are the first detailed electrophysiological characterization of depletion-activated Ca2+ current in nondialyzed cells. Because exogenous molecules and channels are easy to introduce into oocytes and the distortions in measuring ICl(Ca) can now be bypassed, oocytes are now a superior system in which to analyze the activation mechanisms of capacitative Ca2+ influx.

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Discovery and characterization of Hv1-type proton channels in reef-building corals.

10.1101/2021.04.08.439075 ◽

2021 ◽

Author(s):

Gisela Rangel-Tescas ◽

Cecilia Cervantes ◽

Miguel A Cervantes-Rocha ◽

Esteban Suarez-Delgado ◽

Anastazia T Banaszak ◽

...

Keyword(s):

Voltage Dependence ◽

Ph Regulation ◽

Functional Characterization ◽

Gene Encoding ◽

Proton Channels ◽

Gating Model ◽

Mechanistic Insight ◽

Voltage Dependent ◽

Insight Into

Voltage-dependent proton-permeable channels are membrane proteins mediating a number of important physiological functions. Here we report the presence of a gene encoding for Hv1 voltage-dependent, proton-permeable channels in two species of reef-building corals. We performed a characterization of their biophysical properties and found that these channels are fast-activating and modulated by the pH gradient in a manner that makes them interesting models for studying these processes more easily. We have also developed an allosteric gating model that provides mechanistic insight into the modulation of voltage-dependence by protons. This work also represents the first functional characterization of any ion channel in scleractinian corals. We discuss the implications of the presence of these channels in the membranes of coral cells in the calcification and pH regulation processes and possible consequences of ocean acidification related to the function of these channels.

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