scholarly journals Divalent cation selectivity for external block of voltage-dependent Na+ channels prolonged by batrachotoxin. Zn2+ induces discrete substates in cardiac Na+ channels.

1991 ◽  
Vol 97 (1) ◽  
pp. 89-115 ◽  
Author(s):  
A Ravindran ◽  
L Schild ◽  
E Moczydlowski
Keyword(s):  
Surface Charge ◽  
Voltage Dependence ◽  
Divalent Cations ◽  
Na Channel ◽  
Canine Heart ◽  
Na Channels ◽  
Cation Selectivity ◽  
Voltage Dependent ◽  
Negative Surface ◽  
Negative Surface Charge

The mechanism of block of voltage-dependent Na+ channels by extracellular divalent cations was investigated in a quantitative comparison of two distinct Na+ channel subtypes incorporated into planar bilayers in the presence of batrachotoxin. External Ca2+ and other divalent cations induced a fast voltage-dependent block observed as a reduction in unitary current for tetrodotoxin-sensitive Na+ channels of rat skeletal muscle and tetrodotoxin-insensitive Na+ channels of canine heart ventricular muscle. Using a simple model of voltage-dependent binding to a single site, these two distinct Na+ channel subtypes exhibited virtually the same affinity and voltage dependence for fast block by Ca2+ and a number of other divalent cations. This group of divalent cations exhibited an affinity sequence of Co congruent to Ni greater than Mn greater than Ca greater than Mg greater than Sr greater than Ba, following an inverse correlation between binding affinity and ionic radius. The voltage dependence of fast Ca2+ block was essentially independent of CaCl2 concentration; however, at constant voltage the Ca2+ concentration dependence of fast block deviated from a Langmuir isotherm in the manner expected for an effect of negative surface charge. Titration curves for fast Ca2+ block were fit to a simplified model based on a single Ca2+ binding site and the Gouy-Chapman theory of surface charge. This model gave similar estimates of negative surface charge density in the vicinity of the Ca2+ blocking site for muscle and heart Na+ channels. In contrast to other divalent cations listed above, Cd2+ and Zn2+ are more potent blockers of heart Na+ channels than muscle Na+ channels. Cd2+ induced a fast, voltage-dependent block in both Na+ channel subtypes with a 46-fold higher affinity at 0 mV for heart (KB = 0.37 mM) vs. muscle (KB = 17 mM). Zn2+ induced a fast, voltage-dependent block of muscle Na+ channels with low affinity (KB = 7.5 mM at 0 mV). In contrast, micromolar Zn2+ induced brief closures of heart Na+ channels that were resolved as discrete substate events at the single-channel level with an apparent blocking affinity of KB = 0.067 mM at 0 mV, or 110-fold higher affinity for Zn2+ compared with the muscle channel. High-affinity block of the heart channel by Cd2+ and Zn2+ exhibited approximately the same voltage dependence (e-fold per 60 mV) as low affinity block of the muscle subtype (e-fold per 54 mV), suggesting that the block occurs at structurally analogous sites in the two Na+ channels.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals Kinetics of 9-aminoacridine block of single Na channels.

1984 ◽  
Vol 84 (3) ◽  
pp. 361-377 ◽  
Author(s):  
D Yamamoto ◽  
J Z Yeh
Keyword(s):  
Rate Constant ◽  
Voltage Dependence ◽  
Single Channel ◽  
Na Channel ◽  
Na Channels ◽  
Patch Clamp Technique ◽  
Open Time ◽  
Voltage Dependent ◽  
The Mean ◽  
Kinetics Of

The kinetics of 9-aminoacridine (9-AA) block of single Na channels in neuroblastoma N1E-115 cells were studied using the gigohm seal, patch clamp technique, under the condition in which the Na current inactivation had been eliminated by treatment with N-bromoacetamide (NBA). Following NBA treatment, the current flowing through individual Na channels was manifested by square-wave open events lasting from several to tens of milliseconds. When 9-AA was applied to the cytoplasmic face of Na channels at concentrations ranging from 30 to 100 microM, it caused repetitive rapid transitions (flickering) between open and blocked states within single openings of Na channels, without affecting the amplitude of the single channel current. The histograms for the duration of blocked states and the histograms for the duration of open states could be fitted with a single-exponential function. The mean open time (tau o) became shorter as the drug concentration was increased, while the mean blocked time (tau b) was concentration independent. The association (blocking) rate constant, kappa, calculated from the slope of the curve relating the reciprocal mean open time to 9-AA concentration, showed little voltage dependence, the rate constant being on the order of 1 X 10(7) M-1s-1. The dissociation (unblocking) rate constant, l, calculated from the mean blocked time, was strongly voltage dependent, the mean rate constant being 214 s-1 at 0 mV and becoming larger as the membrane being hyperpolarized. The voltage dependence suggests that a first-order blocking site is located at least 63% of the way through the membrane field from the cytoplasmic surface. The equilibrium dissociation constant for 9-AA to block the Na channel, defined by the relation of l/kappa, was calculated to be 21 microM at 0 mV. Both tau -1o and tau -1b had a Q10 of 1.3, which suggests that binding reaction was diffusion controlled. The burst time in the presence of 9-AA, which is the sum of open times and blocked times, was longer than the lifetime of open channels in the absence of drug. All of the features of 9-AA block of single Na channels are compatible with the sequential model in which 9-AA molecules block open Na channels, and the blocked channels could not close until 9-AA molecules had left the blocking site in the channels.

Meperidine and Lidocaine Block of Recombinant Voltage-Dependent Na+Channels 

1999 ◽  
Vol 91 (5) ◽  
pp. 1481-1481 ◽  
Author(s):  
Larry E. Wagner ◽  
Michael Eaton ◽  
Salas S. Sabnis ◽  
Kevin J. Gingrich
Keyword(s):  
Steady State ◽  
Local Anesthesia ◽  
Local Anesthetic ◽  
Voltage Dependence ◽  
Tonic Inhibition ◽  
Na Channel ◽  
Mutant Form ◽  
Na Channels ◽  
Voltage Dependent ◽  
Steady State Inactivation

Background The opioid meperidine induces spinal anesthesia and blocks nerve action potentials, suggesting it is a local anesthetic. However, whether it produces effective clinical local anesthesia in peripheral nerves remains unclear. Classification as a local anesthetic requires clinical local anesthesia but also blockade of voltage-dependent Na+ channels with characteristic features (tonic and phasic blockade and a negative shift in the voltage-dependence of steady-state inactivation) involving an intrapore receptor. The authors tested for these molecular pharmacologic features to explore whether meperidine is a local anesthetic. Methods The authors studied rat skeletal muscle mu1 (RSkM1) voltage-dependent Na+ channels or a mutant form heterologously coexpressed with rat brain Na+ channel accessory beta1, subunit in Xenopus oocytes. Polymerase chain reaction was used for mutagenesis, and mutations were confirmed by sequencing. Na+ currents were measured using a two-microelectrode voltage clamp. Meperidine and the commonly used local anesthetic lidocaine were applied to oocytes in saline solution at room temperature. Results Meperidine and lidocaine produced tonic current inhibition with comparable concentration dependence. Meperidine caused phasic current inhibition in which the concentration-response relationship was shifted to fivefold greater concentration relative to lidocaine. Meperidine and lidocaine negatively shifted the voltage dependence of steady-state inactivation. Mutation of a putative local anesthetic receptor reduced phasic inhibition by meperidine and lidocaine and tonic inhibition by lidocaine, but not meperidine tonic inhibition. Conclusions Meperidine blocks Na+ channels with molecular pharmacologic features of a local anesthetic. The findings support classification of meperidine as a local anesthetic but with less overall potency than lidocaine.

scholarly journals Voltage-dependent open-state inactivation of cardiac sodium channels: gating current studies with Anthopleurin-A toxin.

1995 ◽  
Vol 106 (4) ◽  
pp. 617-640 ◽  
Author(s):  
M F Sheets ◽  
D A Hanck
Keyword(s):  
Time Course ◽  
Voltage Dependence ◽  
Na Channel ◽  
Total Charge ◽  
Na Channels ◽  
Gating Currents ◽  
Gating Charge ◽  
Cardiac Purkinje Cells ◽  
Voltage Dependent ◽  
Cardiac Sodium Channels

The gating charge and voltage dependence of the open state to the inactivated state (O-->I) transition was measured for the voltage-dependent mammalian cardiac Na channel. Using the site 3 toxin, Anthopleurin-A (Ap-A), which selectively modifies the O-->I transition (see Hanck, D. A., and M. F. Sheets. 1995. Journal of General Physiology. 106:601-616), we studied Na channel gating currents (Ig) in voltage-clamped single canine cardiac Purkinje cells at approximately 12 degrees C. Comparison of Ig recorded in response to step depolarizations before and after modification by Ap-A toxin showed that toxin-modified gating currents decayed faster and had decreased initial amplitudes. The predominate change in the charge-voltage (Q-V) relationship was a reduction in gating charge at positive potentials such that Qmax was reduced by 33%, and the difference between charge measured in Ap-A toxin and in control represented the gating charge associated with Na channels undergoing inactivation by O-->I. By comparing the time course of channel activation (represented by the gating charge measured in Ap-A toxin) and gating charge associated with the O-->I transition (difference between control and Ap-A charge), the influence of activation on the time course of inactivation could be accounted for and the inherent voltage dependence of the O-->I transition determined. The O-->I transition for cardiac Na channels had a valence of 0.75 e-. The total charge of the cardiac voltage-gated Na channel was estimated to be 5 e-. Because charge is concentrated near the opening transition for this isoform of the channel, the time constant of the O-->I transition at 0 mV could also be estimated (0.53 ms, approximately 12 degrees C). Prediction of the mean channel open time-voltage relationship based upon the magnitude and valence of the O-->C and O-->I rate constants from INa and Ig data matched data previously reported from single Na channel studies in heart at the same temperature.

scholarly journals Agonist-specific voltage-dependent gating of lysosomal two-pore Na+ channels

eLife ◽  
2019 ◽  
Vol 8 ◽  
Author(s):  
Xiaoli Zhang ◽  
Wei Chen ◽  
Ping Li ◽  
Raul Calvo ◽  
Noel Southall ◽  
...  
Keyword(s):  
Small Molecule ◽  
Membrane Trafficking ◽  
High Throughput Screening ◽  
Voltage Dependence ◽  
Na Channel ◽  
Dependent Manner ◽  
Na Channels ◽  
Channel Activity ◽  
Ph Homeostasis ◽  
Voltage Dependent

Mammalian two-pore-channels (TPC1, 2; TPCN1, TPCN2) are ubiquitously- expressed, PI(3,5)P2-activated, Na+-selective channels in the endosomes and lysosomes that regulate luminal pH homeostasis, membrane trafficking, and Ebola viral infection. Whereas the channel activity of TPC1 is strongly dependent on membrane voltage, TPC2 lacks such voltage dependence despite the presence of the presumed ‘S4 voltage-sensing’ domains. By performing high-throughput screening followed by lysosomal electrophysiology, here we identified a class of tricyclic anti-depressants (TCAs) as small-molecule agonists of TPC channels. TCAs activate both TPC1 and TPC2 in a voltage-dependent manner, referred to as Lysosomal Na+ channel Voltage-dependent Activators (LyNa-VAs). We also identified another compound which, like PI(3,5)P2, activates TPC2 independent of voltage, suggesting the existence of agonist-specific gating mechanisms. Our identification of small-molecule TPC agonists should facilitate the studies of the cell biological roles of TPCs and can also readily explain the reported effects of TCAs in the modulation of autophagy and lysosomal functions.

Fast and Slow Activation Kinetics of Voltage-Gated Sodium Channels in Molluscan Neurons

1997 ◽  
Vol 77 (5) ◽  
pp. 2373-2384 ◽  
Author(s):  
William F. Gilly ◽  
Rhanor Gillette ◽  
Matthew McFarlane
Keyword(s):  
Sodium Channels ◽  
Voltage Dependence ◽  
Na Channel ◽  
Molluscan Neurons ◽  
Na Channels ◽  
Activation Kinetics ◽  
Voltage Gated ◽  
Voltage Gated Sodium Channels ◽  
Voltage Dependent ◽  
Kinetics Of

Gilly, William F., Rhanor Gillette, and Matthew McFarlane. Fast and slow activation kinetics of voltage-gated sodium channels in molluscan neurons. J. Neurophysiol. 77: 2373–2384, 1997. Whole cell patch-clamp recordings of Na current ( I Na) were made under identical experimental conditions from isolated neurons from cephalopod ( Loligo, Octopus) and gastropod ( Aplysia, Pleurobranchaea, Doriopsilla) species to compare properties of activation gating. Voltage dependence of peak Na conductance ( g Na) is very similar in all cases, but activation kinetics in the gastropod neurons studied are markedly slower. Kinetic differences are very pronounced only over the voltage range spanned by the g Na-voltage relation. At positive and negative extremes of voltage, activation and deactivation kinetics of I Na are practically indistinguishable in all species studied. Voltage-dependent rate constants underlying activation of the slow type of Na channel found in gastropods thus appear to be much more voltage dependent than are the equivalent rates in the universally fast type of channel that predominates in cephalopods. Voltage dependence of inactivation kinetics shows a similar pattern and is representative of activation kinetics for the two types of Na channels. Neurons with fast Na channels can thus make much more rapid adjustments in the number of open Na channels at physiologically relevant voltages than would be possible with only slow Na channels. This capability appears to be an adaptation that is highly evolved in cephalopods, which are well known for their high-speed swimming behaviors. Similarities in slow and fast Na channel subtypes in molluscan and mammalian neurons are discussed.

Surface charge and extracellular polymer of sludge in the anaerobic degradation process

1996 ◽  
Vol 34 (5-6) ◽  
pp. 309-316 ◽  
Author(s):  
X. S. Jia ◽  
Herbert H. P. Fang ◽  
H. Furumai
Keyword(s):  
Surface Charge ◽  
Growth Phase ◽  
Anaerobic Degradation ◽  
Degradation Process ◽  
Anaerobic Sludge ◽  
Batch Experiments ◽  
High Substrate Concentration ◽  
Negative Surface ◽  
Negative Surface Charge ◽  
Extracellular Polymer

Changes of surface charge and extracellular polymer (ECP) content were investigated in batch experiments for three anaerobic sludges, each of which had been enriched at 35°C and pH 639-7.3 for more than 40 batches using propionate, butyrate and glucose, individually, as the sole substrate. Results showed that both ECP and the negative surface charge were dependent on the growth phase of microorganisms. They increased at the beginning of all batches when the microorganisms were in the prolific-growth phase, having high substrate concentration and food-to-microorganisms ratio. Both later gradually returned to their initial levels when the microorganisms were in the declined-growth phase, as the substrate became depleted. The negative surface charge increased linearly with the total-ECP content in all series with slopes of 0.0187, 0.0212 and 0.0157 meq/mg-total-ECP for sludge degrading propionate, butyrate and glucose, respectively. The change of surface charge for the first two sludges was mainly due to the increase of proteinaceous fraction of ECP; but, for glucose-degrading sludge, that could be due to the increases of both proteinaceous and carbohydrate fractions of ECP. The negative-charged nature of anaerobic sludge implies that cations should be able to promote granulation of anaerobic sludge.

scholarly journals Nanoemulsions for the Encapsulation of Hydrophobic Actives

Cosmetics ◽  
2021 ◽  
Vol 8 (2) ◽  
pp. 45
Author(s):  
Eduardo Guzmán ◽  
Laura Fernández-Peña ◽  
Lorenzo Rossi ◽  
Mathieu Bouvier ◽  
Francisco Ortega ◽  
...  
Keyword(s):  
Surface Charge ◽  
Long Term Stability ◽  
Promising Tool ◽  
Oil In Water ◽  
Nanometric Range ◽  
Negative Surface ◽  
Negative Surface Charge ◽  
Highly Hydrophobic ◽  
Technological Interest

This work analyzes the dispersion of two highly hydrophobic actives, (9Z)-N-(1,3-dihydroxyoctadecan-2-yl)octadec-9-enamide (ceramidelike molecule) and 2,6-diamino-4-(piperidin-1-yl)pyrimidine 1-oxide (minoxidil), using oil-in-water nanoemulsions with the aim of preparing stable and safe aqueous-based formulations that can be exploited for enhancing the penetration of active compounds through cosmetic substrates. Stable nanoemulsions with a droplet size in the nanometric range (around 200 nm) and a negative surface charge were prepared. It was possible to prepare formulations containing up to 2 w/w% of ceramide-like molecules and more than 10 w/w% of minoxidil incorporated within the oil droplets. This emulsions evidenced a good long-term stability, without any apparent modification for several weeks. Despite the fact that this work is limited to optimize the incorporation of the actives within the nanoemulsion-like formulations, it demonstrated that nanoemulsions should be considered as a very promising tool for enhancing the distribution and availability of hydrophobic molecules with technological interest.

SURFACE-CHARGE-ENABLED PHOTOLYTIC HYDROGEN GENERATION IN V2O5·H2O/Au NANOCONJUGATES

MRS Advances ◽  
2016 ◽  
Vol 1 (46) ◽  
pp. 3121-3126
Author(s):  
Sunith Varghese ◽  
Charuksha Walgama ◽  
Mark Wilkins ◽  
Sadagopan Krishnan ◽  
Kaan Kalkan
Keyword(s):  
Surface Charge ◽  
Hydrogen Generation ◽  
Hydrogen Reduction ◽  
Energy Levels ◽  
Sol Gel ◽  
Band Edge ◽  
Conduction Band Edge ◽  
Current Voltage ◽  
Negative Surface ◽  
Negative Surface Charge

ABSTRACTThe present work investigates sol-gel synthesized vanadium oxyhydrate (V2O5·H2O) nanowires decorated with Au nanoparticles as potential photolytic H2 generators. As determined by UV photoelectron and optical spectroscopies, the conduction band edge of V2O5·H2O lies 0.6 eV below standard H+ reduction potential, implying no H2 can be generated. On the contrary, as measured by gas chromatography, our nanoconjugates yield reproducible light-to-hydrogen conversion efficiency of 5.3%, for the first hour of photolysis under 470 nm excitation. To explain the observed hydrogen reduction, we have hypothesized the vanadia electron energy levels are raised by some negative surface charge. With the objective of validating this hypothesis, we have performed cyclic current-voltage measurements. The derived conduction and valence band edge energies are not only consistent with the optical band gaps, but also validate the hypothesized energy increase by 1.6 eV, respectively. The negative surface charge is also corroborated by the ζ-potential. Based on the measured pH of 2.4, we attribute the negative surface charge to Lewis acid nature of the nanowires, establishing dative bonding with OH−. The present work establishes the importance of surface charge in photoelectrochemical reactions, where it can be instrumental and enabling in photolytic fuel production.

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