scholarly journals Conduction through the Inward Rectifier Potassium Channel, Kir2.1, Is Increased by Negatively Charged Extracellular Residues

2005 ◽  
Vol 125 (5) ◽  
pp. 493-503 ◽  
Author(s):  
Nazzareno D'Avanzo ◽  
Hee Cheol Cho ◽  
Illya Tolokh ◽  
Roman Pekhletski ◽  
Igor Tolokh ◽  
...  
Keyword(s):  
Surface Charge ◽  
Single Channel ◽  
Molecular Model ◽  
Chinese Hamster ◽  
Fluctuation Analysis ◽  
Channel Measurements ◽  
Surface Charges ◽  
Charge Effects ◽  
Current Decay ◽  
Inward Rectifier Potassium Channel

Ion channel conductance can be influenced by electrostatic effects originating from fixed “surface” charges that are remote from the selectivity filter. To explore whether surface charges contribute to the conductance properties of Kir2.1 channels, unitary conductance was measured in cell-attached recordings of Chinese hamster ovary (CHO) cells transfected with Kir2.1 channels over a range of K+ activities (4.6–293.5 mM) using single-channel measurements as well as nonstationary fluctuation analysis for low K+ activities. K+ ion concentrations were shown to equilibrate across the cell membrane in our studies using the voltage-sensitive dye DiBAC4(5). The dependence of γ on the K+ activity (aK) was fit well by a modified Langmuir binding isotherm, with a nonzero intercept as aK approaches 0 mM, suggesting electrostatic surface charge effects. Following the addition of 100 mM N-methyl-d-glucamine (NMG+), a nonpermeant, nonblocking cation or following pretreatment with 50 mM trimethyloxonium (TMO), a carboxylic acid esterifying agent, the γ–aK relationship did not show nonzero intercepts, suggesting the presence of surface charges formed by glutamate or aspartate residues. Consistent with surface charges in Kir2.1 channels, the rates of current decay induced by Ba2+ block were slowed with the addition of NMG or TMO. Using a molecular model of Kir2.1 channels, three candidate negatively charged residues were identified near the extracellular mouth of the pore and mutated to cysteine (E125C, D152C, and E153C). E153C channels, but not E125C or D152C channels, showed hyperbolic γ–aK relationships going through the origin. Moreover, the addition of MTSES to restore the negative charges in E53C channels reestablished wild-type conductance properties. Our results demonstrate that E153 contributes to the conductance properties of Kir2.1 channels by acting as a surface charge.

scholarly journals Effect of Salicylate on KCNQ4 of the Guinea Pig Outer Hair Cell

2010 ◽  
Vol 103 (4) ◽  
pp. 1969-1977 ◽  
Author(s):  
T. Wu ◽  
P. Lv ◽  
H. J. Kim ◽  
E. N. Yamoah ◽  
A. L. Nuttall
Keyword(s):  
Hearing Loss ◽  
Animal Studies ◽  
Outer Hair Cell ◽  
Single Channel ◽  
Chinese Hamster ◽  
Outer Hair Cells ◽  
Fluctuation Analysis ◽  
High Dose ◽  
Voltage Sensitivity ◽  
Physiological Concentration

Salicylate causes a moderate hearing loss and tinnitus in humans at high-dose levels. Salicylate-induced hearing loss has been attributed to impaired sound amplification by outer hair cells (OHCs) through its direct action on the OHC motility sensor and/or motor. However, there is a disparity of salicylate concentrations between the clinical and animal studies, i.e., extremely high extracellular concentrations of salicylate (from 1 to 10 mM) is required to produce a significant reduction of electromotility in animal studies. Such concentrations are above the clinical/physiological range for humans. Here, we showed that clinical/physiological concentration range of salicylate caused concentration-dependent and reversible reductions in IK,n (KCNQ4) and subsequent depolarization of OHCs. Salicylate reduced the maximal tail current of the activation curve of IK,n without altering the voltage-sensitivity ( Vhalf). The salicylate-induced reduction of IK,n was almost completely blocked by linopirdine (0.1 mM) and BaCl2 (10 mM). Consistent with the finding in OHCs, salicylate significantly reduced KCNQ4-mediated current expressed in Chinese hamster ovarian (CHO) cells by comparable amplitude to OHCs without significantly shifting Vhalf. Nonstationary fluctuation analysis shows that salicylate significantly reduced the estimated single-channel current amplitude and numbers. Intracellular Ca2+ elevation resulting from cytoplasmic acidosis also contributes to the current reduction of IK,n (KCNQ4) of OHCs. These results indicate a different model for the salicylate-induced hearing loss through the reduction of KCNQ4 and subsequent depolarization of OHCs, which reduces the driving force for transduction current and electromotility. The major mechanism underlying the reduction of IK,n (KCNQ4) is the direct blocking action of salicylate on KCNQ4.

scholarly journals Modulation of the T-type cardiac Ca channel by changes in proton concentration.

1990 ◽  
Vol 96 (5) ◽  
pp. 973-990 ◽  
Author(s):  
J Tytgat ◽  
B Nilius ◽  
E Carmeliet
Keyword(s):  
Single Channel ◽  
Ca Channel ◽  
Channel Measurements ◽  
Surface Charges ◽  
Maximal Conductance ◽  
Whole Cell ◽  
Pka Values ◽  
Channel Modulation ◽  
Proton Concentration ◽  
Negative Surface

Single-channel measurements and whole-cell experiments with the two suction electrode, voltage clamp technique were used to investigate the effects of external and internal proton concentrations on T-type Ca channels in heart muscle cells of the guinea pig. As in the L-type Ca channel, an increase in the external proton concentration decreases T-type currents, while external alkalinization enlarges the currents. In contrast to the L-type Ca channel, however, a change in the internal proton concentration does not modulate T-type Ca currents. The T-type Ca channel is much more sensitive to variations in pHo than the L-type Ca channel. By the combination of single-channel and whole-cell experiments we can conclude that the observed changes in macroscopic currents are due to (a) changes in the single-channel conductance and in the probability of the T-type Ca channel being open, and (b) the titration of the negative surface charges in the neighborhood of the T-type Ca channel with shifts of both the activation and inactivation processes of the channel. The pHo-induced changes in the maximal conductance (gmax) of the T-type Ca channel show an apparent pKa in the range of 7.1-7.5, while the titration of the negative surface charges near the channel shows an apparent pKa of 7.1 with a concomitant surface potential of -24.6 mV at 5.4 mM [Ca]o. These pKa values, less acid than the pKa values found for the pHo-induced, L-type Ca channel modulation, might imply a physiological importance of this novel type of channel modulation.

scholarly journals Photoluminescence of Fully Inorganic Colloidal Gold Nanocluster and Their Manipulation Using Surface Charge Effects

2021 ◽  
pp. 2101549
Author(s):  
Anna R. Ziefuss ◽  
Torben Steenbock ◽  
Dominik Benner ◽  
Anton Plech ◽  
Jörg Göttlicher ◽  
...  
Keyword(s):  
Surface Charge ◽  
Colloidal Gold ◽  
Gold Nanocluster ◽  
Charge Effects

Electric field tomography: setup for single-channel measurements

2007 ◽  
Vol 28 (7) ◽  
pp. S279-S289 ◽  
Author(s):  
A V Korjenevsky ◽  
T S Tuykin
Keyword(s):  
Electric Field ◽  
Single Channel ◽  
Channel Measurements

scholarly journals Insulation of the conduction pathway of muscle transverse tubule calcium channels from the surface charge of bilayer phospholipid.

1986 ◽  
Vol 87 (6) ◽  
pp. 933-953 ◽  
Author(s):  
R Coronado ◽  
H Affolter
Keyword(s):  
Ionic Strength ◽  
Calcium Channels ◽  
Calcium Channel ◽  
Surface Charge ◽  
Single Channel ◽  
Small Surface ◽  
Bilayer Lipid ◽  
Sodium Conductance ◽  
Conduction Pathway ◽  
Lipid Surface

Functional calcium channels present in purified skeletal muscle transverse tubules were inserted into planar phospholipid bilayers composed of the neutral lipid phosphatidylethanolamine (PE), the negatively charged lipid phosphatidylserine (PS), and mixtures of both. The lengthening of the mean open time and stabilization of single channel fluctuations under constant holding potentials was accomplished by the use of the agonist Bay K8644. It was found that the barium current carried through the channel saturates as a function of the BaCl2 concentration at a maximum current of 0.6 pA (at a holding potential of 0 mV) and a half-saturation value of 40 mM. Under saturation, the slope conductance of the channel is 20 pS at voltages more negative than -50 mV and 13 pS at a holding potential of 0 mV. At barium concentrations above and below the half-saturation point, the open channel currents were independent of the bilayer mole fraction of PS from XPS = 0 (pure PE) to XPS = 1.0 (pure PS). It is shown that in the absence of barium, the calcium channel transports sodium or potassium ions (P Na/PK = 1.4) at saturating rates higher than those for barium alone. The sodium conductance in pure PE bilayers saturates as a function of NaCl concentration, following a curve that can be described as a rectangular hyperbola with a half-saturation value of 200 mM and a maximum conductance of 68 pS (slope conductance at a holding potential of 0 mV). In pure PS bilayers, the sodium conductance is about twice that measured in PE at concentrations below 100 mM NaCl. The maximum channel conductance at high ionic strength is unaffected by the lipid charge. This effect at low ionic strength was analyzed according to J. Bell and C. Miller (1984. Biophysical Journal. 45:279-287) and interpreted as if the conduction pathway of the calcium channel were separated from the bilayer lipid by approximately 20 A. This distance thereby effectively insulates the ion entry to the channel from the bulk of the bilayer lipid surface charge. Current vs. voltage curves measured in NaCl in pure PE and pure PS show that similarly small surface charge effects are present in both inward and outward currents. This suggests that the same conduction insulation is present at both ends of the calcium channel.

Ts65Dn, a Mouse Model of Down Syndrome, Exhibits Increased GABAB-Induced Potassium Current

2007 ◽  
Vol 97 (1) ◽  
pp. 892-900 ◽  
Author(s):  
Tyler K. Best ◽  
Richard J. Siarey ◽  
Zygmunt Galdzicki
Keyword(s):  
Down Syndrome ◽  
Mouse Model ◽  
Hippocampal Neurons ◽  
Single Channel ◽  
Extra Chromosome ◽  
Functional Expression ◽  
Chromosome 21 ◽  
Fluctuation Analysis ◽  
Response Curves ◽  
Girk Channel

Down syndrome (DS) is the most common nonheritable cause of mental retardation. DS is the result of the presence of an extra chromosome 21 and its phenotype may be a consequence of overexpressed genes from that chromosome. One such gene is Kcnj6/Girk2, which encodes the G-protein-coupled inward rectifying potassium channel subunit 2 (GIRK2). We have recently shown that the DS mouse model, Ts65Dn, overexpresses GIRK2 throughout the brain and in particular the hippocampus. Here we report that this overexpression leads to a significant increase (∼2-fold) in GABAB-mediated GIRK current in primary cultured hippocampal neurons. The dose response curves for peak and steady-state GIRK current density is significantly shifted left toward lower concentrations of baclofen in Ts65Dn neurons compared with diploid controls, consistent with increased functional expression of GIRK channels. Stationary fluctuation analysis of baclofen-induced GIRK current from Ts65Dn neurons indicated no significant change in single-channel conductance compared with diploid. However, significant increases in GIRK channel density was found in Ts65Dn neurons. In normalized baclofen-induced GIRK current and GIRK current kinetics no difference was found between diploid and Ts65Dn neurons, which suggests unimpaired mechanisms of interaction between GIRK channel and GABAB receptor. These results indicate that increased expression of GIRK2 containing channels have functional consequences that likely affect the balance between excitatory and inhibitory neuronal transmission.

scholarly journals Water Dynamics in Hydrated Carboxylated Cellulose Nanofibril Membranes

2019 ◽  
Author(s):  
Shun Yu ◽  
Valentina Guccini ◽  
Franz Demmel ◽  
Germán Salazar-Alvarez
Keyword(s):  
Surface Charge ◽  
Network Formation ◽  
Water Movement ◽  
Polymer Electrolyte Membrane ◽  
Cellulose Nanofibrils ◽  
Bulk Water ◽  
Water Dynamics ◽  
Surface Charges ◽  
Tempo Oxidation ◽  
Elastic Neutron

Cellulose nanofibrils (CNF) are a class of materials with good mechanical properties, surface functionality and bio-/environmental friendliness. They have been used in many applications as loading material or function materials, where water-cellulose interaction determines the materials performance. Especially, CNF with carboxylated groups can be used as the separation membrane in polymer electrolyte membrane fuel cell. The water dynamics is closely related to the proton conductivity. The Non-destructive quasi-elastic neutron scattering (QENS) is used to characterized water movement in hydrated membrane made of CNF prepared by TEMPO-oxidation with different surface charges. However, neither surface charge nor the nanoconfinement due to membrane swelling has large impact on water dynamics mechanism. A slow diffusive motion is found with the diffusion coefficient close to bulk water and that in hydrated Nafion membrane regardless the surface charge, while a fast motion is rather localized with a correlation time increasing as temperature increase, which might related to the hydrogen bond network formation between water and CNF.

scholarly journals Local and correlated studies of humidity-mediated ferroelectric thin film surface charge dynamics

2021 ◽  
Vol 7 (1) ◽  
Author(s):  
Iaroslav Gaponenko ◽  
Loïc Musy ◽  
Neus Domingo ◽  
Nicolas Stucki ◽  
Albert Verdaguer ◽  
...  
Keyword(s):  
Surface Charge ◽  
Dictionary Learning ◽  
Film Surface ◽  
Ferroelectric Thin Film ◽  
Microscopy Study ◽  
Lateral Spread ◽  
Surface Charges ◽  
Kelvin Probe ◽  
Sensing Applications ◽  
Reaction Diffusion Model

AbstractElectrochemical phenomena in ferroelectrics are of particular interest for catalysis and sensing applications, with recent studies highlighting the combined role of the ferroelectric polarisation, applied surface voltage and overall switching history. Here, we present a systematic Kelvin probe microscopy study of the effect of relative humidity and polarisation switching history on the surface charge dissipation in ferroelectric Pb(Zr0.2Ti0.8)O3 thin films. We analyse the interaction of surface charges with ferroelectric domains through the framework of physically constrained unsupervised machine learning matrix factorisation, Dictionary Learning, and reveal a complex interplay of voltage-mediated physical processes underlying the observed signal decays. Additional insight into the observed behaviours is given by a Fitzhugh–Nagumo reaction–diffusion model, highlighting the lateral spread and charge passivation process contributors within the Dictionary Learning analysis.

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