scholarly journals Ionic Conductance Changes in Voltage Clamped Crayfish Axons at Low pH

1974 ◽  
Vol 64 (6) ◽  
pp. 666-690 ◽  
Author(s):  
Peter Shrager
Keyword(s):  
Surface Charge ◽  
Potassium Conductance ◽  
Potassium Currents ◽  
Ionic Currents ◽  
Low Ph ◽  
Giant Axons ◽  
Voltage Curve ◽  
Conductance Changes ◽  
Membrane Components ◽  
Wire System

Giant axons from the crayfish have been voltage clamped with an axial wire system. General characterististics of observed ionic currents under normal conditions are similar to those measured in other giant axons and in nodes of Ranvier. As the pH of the external bath is lowered below 7, a marked, reversible slowing of potassium currents is seen with little effect on sodium currents. The steady-state potassium conductance-voltage curve is shifted along the voltage axis in a manner consistent with the development of a hyperpolarizing surface charge. Results suggest that this potential shift accounts for part, though not all, of the observed increase in τn. From the behavior of the kinetics of the delayed current with external pH these alterations in potassium conductance are attributed to the titration of a histidine imidazole residue of a membrane protein. Chemical modification of histidine by carbethoxylation at pH 6 slows and strongly depresses potassium currents. The results suggest that in addition to the introduction of electrostatic forces, possibly resulting from a hyperpolarizing surface charge, protonation of a histidine group at low pH also alters the nonelectrostatic chemical interactions determining the ease with which potassium gates open and close. The evidence indicates that the modified histidine residue is closely associated with the membrane components involved in the control of potassium conductance.

scholarly journals Magnitude and location of surface charges on Myxicola giant axons.

1975 ◽  
Vol 66 (1) ◽  
pp. 47-65 ◽  
Author(s):  
T Begenisich
Keyword(s):  
Charge Density ◽  
Surface Charge ◽  
Surface Charge Density ◽  
Potassium Conductance ◽  
Electronic Charge ◽  
Surface Charges ◽  
Giant Axons ◽  
Current Voltage ◽  
Instantaneous Current ◽  
Sodium And Potassium

The effects of changes in the concentration of calcium in solutions bathing Myxicola giant axons on the voltage dependence of sodium and potassium conductance and on the instantaneous sodium and potassium current-voltage relations have been measured. The sodium conductance-voltage relation is shifted along the voltage axis by 13 mV in the hyperpolarizing direction for a fourfold decrease in calcium concentration. The potassium conductance-voltage relation is shifted only half as much as that for sodium. There is no effect on the shape of the sodium and potassium instantaneous current-voltage curves: the normal constant-field rectification of potassium currents is maintained and the normal linear relationship of sodium currents is maintained. Considering that shifts in conductances would reflect the presence of surface charges near the gating machinery and that shape changes of instantaneous current-voltage curves would reflect the presence of surface charges near the ionic pores, these results indicate a negative surface charge density of about 1 electronic charge per 120 A2 near the sodium gating machinery, about 1 e/300 A2 for the potassium gating machinery, and much less surface charge near the sodium or potassium pores. There may be some specific binding of calcium to these surface charges with an upper limit on the binding constant of about 0.2 M-1. The differences in surface charge density suggest a spatial separation for these four membrane components.

Blocking of Potassium Currents by Pronase in Perfused Giant Axons

Nature ◽  
1967 ◽  
Vol 215 (5103) ◽  
pp. 850-852 ◽  
Author(s):  
EDUARDO ROJAS ◽  
ILLANI ATWATER
Keyword(s):  
Potassium Currents ◽  
Giant Axons

Abstract 202: In Vitro Effect of Trisulfate Disaccharide on ICa (L-type), INa, IK, and the Na/Ca Exchange Current Recorded From Rat Ventricular Myocytes by Patch Clamp

2020 ◽  
Vol 127 (Suppl_1) ◽  
Author(s):  
Enio R Vasques ◽  
Helena Nader ◽  
Ivarne Tersariol ◽  
Godoy Carlos
Keyword(s):  
Patch Clamp ◽  
Intracellular Calcium ◽  
Ventricular Myocytes ◽  
Potassium Currents ◽  
Ionic Currents ◽  
Exchange Current ◽  
Antiarrhythmic Action ◽  
Rat Ventricular Myocytes ◽  
Adult Rat ◽  
Vitro Effect

Background: Ion channels are pharmacological targets for antiarrhythmic action, and drugs currently used for this purpose are generally not specific to a site of action and may act on several channels and even trigger proarrhythmic phenomena. Trisulfate disaccharide (TD) is an heparin fragment known to act on the sodium calcium exchanger (NCX), reducing intracellular calcium in overload situations and reversing arrhytmias, but its action on other ionic currents is unknown. Objective: To evaluate by patch clamp the action of TD at different concentrations in NCX and ionic currents in situations of intracellular calcium overload. Materials and Methods: Adult rat myocytes were obtained from a sample from ventricles. Currents were measured using the whole-cell variant of the patch clamp method. Creation of voltage clamp pulses and data acquisition was controlled by a computer with pClamp software. Peak inward current amplitude was measured for ion currents. For Na/Ca exchange current a ramp voltage protocol was employed. Three different concentrations of Cai (300nM, 400nM and 600nM) were used in separate experiments. One drug concentration was applied per cell (10, 30 and 100 micromolar each). The current sensitive to 5mM nickel was taken as the Na/Ca exchange current. The effects of TD on the INa, L-type Ca, and the potassium currents, transiente outward current (Ito), inwardly rectifying potassium current (IK1), and sustained current (Isus) recorded from adult rat ventricular myocytes were also examined in the same conditions. Results: TD concentration-dependently increased the inward Na/Ca exchange current in all intracellular calcium concentration. The effects of TD on the INa, L-type Ca, and the potassium currents, Ito, IK1 and Isus was associated with less than 30% mean reduction on any current at the highest concentration of TD tested (100 micromolar) and still below the positive block controls for different channels that is above 40% block. Conclusion: TD acts on NCX under different concentrations used, without affecting other ionic currents, suggesting specificity in the mechanism of action and possibly not exerting a pro-arrhythmic activity, this effect being desirable for its possible use in reversal of cardiac arrhythmias.

Two types of K+ channels at the basolateral membrane of proximal tubule: inhibitory effect of taurine

1999 ◽  
Vol 277 (2) ◽  
pp. F290-F297 ◽  
Author(s):  
Jean-François Noulin ◽  
Emmanuelle Brochiero ◽  
Jean-Yves Lapointe ◽  
Raynald Laprade
Keyword(s):  
Potassium Channels ◽  
Time Constant ◽  
Potassium Conductance ◽  
Single Type ◽  
K Channel ◽  
Open Probability ◽  
Open Time ◽  
Voltage Curve ◽  
Current Voltage ◽  
Current Voltage Curve

The cell-attached configuration of the patch-clamp technique was used to investigate the effects of taurine on the basolateral potassium channels of rabbit proximal convoluted tubule. In the absence of taurine, the previously reported ATP-blockable channel, KATP, was observed in 51% of patches. It is characterized by an inwardly rectifying current-voltage curve with an inward slope conductance of 49 ± 5 pS ( n = 15) and an outward slope conductance of 13 ± 6 pS ( n = 15). The KATP channel open probability ( P o) is low, 0.15 ± 0.06 ( n = 15) at a − V p = −100 mV ( V pis the pipette potential), and increases slightly with depolarization. The gating kinetics are characterized by one open time constant (τo = 5.0 ± 1.9 ms, n = 6) and two closed time constants (τC1 = 5.2 ± 1.5 ms, τC2 = 140 ± 40 ms; n = 6). In 34% of patches, a second type of potassium channel, sK, with distinct properties was recorded. Its current-voltage curve is characterized by a sigmoidal shape, with an inward slope conductance of 12 ± 2 pS ( n = 4). Its P o is voltage independent and averages 0.67 ± 0.03 ( n = 4) at − V p = −80 mV. Both its open time and closed time distributions are described by a single time constant (τo = 96 ± 19 ms, τC = 10.5 ± 3.6 ms; n = 4). Extracellular perfusion of 40 mM taurine fails to affect sK channels, whereas KATP channel P o decreases by 75% (from 0.17 ± 0.06 to 0.04 ± 0.02, n = 7, P < 0.05). In conclusion, the absolute basolateral potassium conductance of rabbit proximal tubules is the resulting combination of, at least, two types of potassium channels of roughly equal importance: a high-conductance low-open probability KATP channel and a low-conductance high-open probability sK channel. The previously described decrease in the basolateral absolute potassium conductance by taurine is, however, mediated by a single type of K channel: the ATP-blockable K channel.

scholarly journals Tetrodotoxin Blockage of Sodium Conductance Increase in Lobster Giant Axons

1964 ◽  
Vol 47 (5) ◽  
pp. 965-974 ◽  
Author(s):  
Toshio Narahashi ◽  
John W. Moore ◽  
William R. Scott
Keyword(s):  
Action Potential ◽  
Potassium Conductance ◽  
Complete Recovery ◽  
Selective Inhibition ◽  
Resting Potential ◽  
Normal Medium ◽  
Giant Axons ◽  
Sodium Conductance ◽  
Puffer Fish ◽  
Conductance Increase

Previous studies suggested that tetrodotoxin, a poison from the puffer fish, blocks conduction of nerve and muscle through its rather selective inhibition of the sodium-carrying mechanism. In order to verify this hypothesis, observations have been made of sodium and potassium currents in the lobster giant axons treated with tetrodotoxin by means of the sucrose-gap voltage-clamp technique. Tetrodotoxin at concentrations of 1 x 10-7 to 5 x 10-9 gm/ml blocked the action potential but had no effect on the resting potential. Partial or complete recovery might have occurred on washing with normal medium. The increase in sodium conductance normally occurring upon depolarization was very effectively suppressed when the action potential was blocked after tetrodotoxin, while the delayed increase in potassium conductance underwent no change. It is concluded that tetrodotoxin, at very low concentrations, blocks the action potential production through its selective inhibition of the sodium-carrying mechanism while keeping the potassium-carrying mechanism intact.

scholarly journals Blockage of Sodium Conductance Increase in Lobster Giant Axon by Tarichatoxin (Tetrodotoxin)

1966 ◽  
Vol 49 (5) ◽  
pp. 977-988 ◽  
Author(s):  
M. Takata ◽  
J. W. Moore ◽  
C. Y. Kao ◽  
F. A. Fuhrman
Keyword(s):  
Potassium Conductance ◽  
Giant Axon ◽  
High Concentration ◽  
Temporal Characteristics ◽  
Giant Axons ◽  
Sodium Conductance ◽  
Puffer Fish ◽  
Conductance Increase

Tarichatoxin, isolated from California newt eggs, has been found to selectively block the increase of sodium conductance associated with excitation in lobster giant axons at nanomolar concentrations. This resulted from a reduction in the amplitude of the conductance increase rather than a change in its temporal characteristics. The normal potassium conductance increase with depolarization is not altered. A high concentration of calcium applied concomitantly with the toxin significantly improves the reversibility of the sodium blocking. This toxin has recently been identified as chemically identical with tetrodotoxin from the puffer fish. Toxins from the two sources are equally effective and are shown to have an action which is distinctly different from that of procaine.

scholarly journals Hysteresis in the Voltage Dependence of HCN Channels

2005 ◽  
Vol 125 (3) ◽  
pp. 305-326 ◽  
Author(s):  
Roope Männikkö ◽  
Shilpi Pandey ◽  
H. Peter Larsson ◽  
Fredrik Elinder
Keyword(s):  
Voltage Dependence ◽  
Rhythmic Activity ◽  
Ionic Currents ◽  
Hcn Channels ◽  
Molecular Conformations ◽  
Gating Charge ◽  
Voltage Curve ◽  
Current Change ◽  
Voltage Hysteresis ◽  
Hcn1 Channels

Hyperpolarization-activated, cyclic nucleotide-gated (HCN) ion channels are important for rhythmic activity in the brain and in the heart. In this study, using ionic and gating current measurements, we show that cloned spHCN channels undergo a hysteresis in their voltage dependence during normal gating. For example, both the gating charge versus voltage curve, Q(V), and the conductance versus voltage curve, G(V), are shifted by about +60 mV when measured from a hyperpolarized holding potential compared with a depolarized holding potential. In addition, the kinetics of the tail current and the activation current change in parallel to the voltage shifts of the Q(V) and G(V) curves. Mammalian HCN1 channels display similar effects in their ionic currents, suggesting that the mammalian HCN channels also undergo voltage hysteresis. We propose a model in which HCN channels transit between two modes. The voltage dependence in the two modes is shifted relative to each other, and the occupancy of the two modes depends on the previous activation of the channel. The shifts in the voltage dependence are fast (τ ≈ 100 ms) and are not accompanied by any apparent inactivation. In HCN1 channels, the shift in voltage dependence is slower in a 100 mM K extracellular solution compared with a 1 mM K solution. Based on these findings, we suggest that molecular conformations similar to slow (C-type) inactivation of K channels underlie voltage hysteresis in HCN channels. The voltage hysteresis results in HCN channels displaying different voltage dependences during different phases in the pacemaker cycle. Computer simulations suggest that voltage hysteresis in HCN channels decreases the risk of arrhythmia in pacemaker cells.

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