scholarly journals Leak Current Rectification in Myxicola Giant Axons

1969 ◽  
Vol 54 (6) ◽  
pp. 755-764 ◽  
Author(s):  
L. Goldman ◽  
L. Binstock
Keyword(s):  
Field Equation ◽  
Membrane Potential ◽  
Resting Membrane Potential ◽  
Constant Field ◽  
Leak Current ◽  
Giant Axons ◽  
Time To Peak ◽  
Zero Current ◽  
Current Voltage ◽  
Current Voltage Curve

Early leak current, i.e. for times similar to the time to peak of the transient current was measured in Myxicola giant axons in the presence of tetrodotoxin. The leak current-voltage relation rectifies, showing more current for strong depolarizing pulses than expected from symmetry around the holding potential. A satisfactory practical approximation for most leak corrections is constant resting conductance. The leak current-voltage curve rectifies less than expected from the constant field equation. These curves cannot be reconstructed by summing the constant field currents for sodium and potassium using a PNa/PK ratio obtained in the usual way, from zero current constant field fits to resting membrane potential data. Nor can they be reconstructed by summing the constant field current for potassium with that for any other single ion. They can be reconstructed, however, by summing the constant field current for potassium with a constant conductance component. It is concluded that the leak current and the resting membrane potential, therefore, are determined by multiple ionic components, at least three and possibly many. Arguments are presented suggesting that ion permeability ratios obtained in the usual way, by fitting the constant field equation to resting membrane potential data should be viewed with skepticism.

Membrane depolarization in PC-12 cells during hypoxia is regulated by an O2-sensitive K+ current

1996 ◽  
Vol 271 (2) ◽  
pp. C658-C665 ◽  
Author(s):  
W. H. Zhu ◽  
L. Conforti ◽  
M. F. Czyzyk-Krzeska ◽  
D. E. Millhorn
Keyword(s):  
Membrane Potential ◽  
Reversal Potential ◽  
Outward Current ◽  
Cell Voltage ◽  
Membrane Depolarization ◽  
Resting Membrane Potential ◽  
Current Clamp ◽  
Pc 12 Cells ◽  
Current Voltage ◽  
K Current

The effects of hypoxia on K+ current (IK), resting membrane potential, and cytosolic free Ca2+ in rat pheochromocytoma (PC-12) cells were studied. Whole cell voltage- and current-clamp experiments were performed to measure IK and membrane potential, respectively. Cytosolic free Ca2+ level was measured using the Ca(2+)-sensitive fluorescent dye fura 2. Depolarizing voltage steps to +50 mV from a holding potential of -90 mV elicited a slowly inactivating, tetraethylammonium chloride-sensitive, and Ca(2+)-insensitive IK that was reversibly inhibited by reduced O2 tension. Graded reduction in PO2 (from 150 to 0 mmHg) induced a graded inhibition of O2-sensitive IK [IK(O2)] up to 46% at 0 mmHg. Moreover, hypoxia induced a 19-mV membrane depolarization and a twofold increase in cytosolic free Ca2+. In Ca(2+)-free condition, inhibition of IK(O2) induced an 8-mV depolarization, suggesting that inhibition of IK(O2) was responsible for initiating depolarization. The effect of reduced PO2 on the current-voltage relationship showed a reduction of outward current and a 14-mV shift in the reversal potential comparable with the amount of depolarization measured in current clamp experiments. Neither Ca(2+)-activated IK nor inwardly rectifying IK are responsible for the hypoxia-induced depolarization. In conclusion, PC-12 cells express an IK(O2), inhibition of which leads to membrane depolarization and increased intracellular Ca2+, making the PC-12 clonal cell line a useful model for studying the molecular and biophysical mechanisms that mediate O2 chemosensitivity.

scholarly journals Relative Ion Permeabilities in the Crayfish Giant Axon Determined from Rapid External Ion Changes

1967 ◽  
Vol 50 (7) ◽  
pp. 1929-1953 ◽  
Author(s):  
Alfred Strickholm ◽  
B. Gunnar Wallin
Keyword(s):  
Membrane Potential ◽  
Potassium Level ◽  
Potassium Concentration ◽  
Giant Axon ◽  
Resting Potential ◽  
Resting Membrane Potential ◽  
Constant Field ◽  
Appreciable Effect ◽  
Ion Concentrations ◽  
External Potassium

The changes in membrane potential of isolated, single crayfish giant axons following rapid shifts in external ion concentrations have been studied. At normal resting potential the immediate change in membrane potential after a variation in external potassium concentration is quite marked compared to the effect of an equivalent chloride change. If the membrane is depolarized by a maintained potassium elevation, the immediate potential change due to a chloride variation becomes comparable to that of an equivalent potassium change. There is no appreciable effect on membrane potential when external sodium is varied, at normal or at a depolarized membrane potential. Starting from the constant field equation, expressions for the permeability ratios PCl/PK, PNa/PK, and for intracellular potassium and chloride concentrations are derived. At normal resting membrane potential, PCl/PK is 0.13 but at a membrane potential of -53 mv (external potassium level increased about five times) it is 0.85. The intracellular concentrations of potassium and chloride are estimated to be 233 and 34 mM, respectively, and it is pointed out that this is not compatible with ions distributed in a Nernst equilibrium across the membrane. It is also stressed that the information given by a plot of membrane potential vs. the logarithm of external potassium concentrations is very limited and rests upon several important assumptions.

Effect of cold temperature on membrane potential responses in opossum esophageal circular muscle

1989 ◽  
Vol 257 (4) ◽  
pp. G637-G643
Author(s):  
D. Kauvar ◽  
J. Crist ◽  
R. K. Goyal
Keyword(s):  
Smooth Muscle ◽  
Membrane Potential ◽  
Circular Muscle ◽  
Electrical Field Stimulation ◽  
Cold Temperature ◽  
Resting Membrane Potential ◽  
Spike Potential ◽  
Circular Smooth Muscle ◽  
Time To Peak ◽  
Proximal Site

The effects of cold temperature on resting membrane potential (RMP) and membrane potential responses to depolarizing electrical current and intramural nerve stimulation were examined in opossum esophageal circular smooth muscle. Intracellular recordings were made in smooth muscle strips obtained from 7 to 8 cm (proximal site) and 1 to 2 cm (distal site) above the lower esophageal sphincter. RMP was not affected by changes in temperature between 34 and 22 degrees C. Cooling caused progressive inhibition of the amplitude and a slight increase in the duration of the spike potential produced by depolarizing current. Cooling did not modify the threshold for spike potential generation but decreased the spike amplitude from 34.0 +/- 0.5 mV at 34 degrees C to 14.1 +/- 2.2 mV at 22 degrees C (P less than 0.01). Electrical field stimulation with single electrical pulses (1.0 ms) produced tetrodotoxin-sensitive biphasic membrane responses consisting of initial hyperpolarization, or an inhibitory junction potential followed by depolarization that increased in amplitude as temperature was decreased from 34 to 26 degrees C and then decreased in amplitude as temperature was further decreased. At both proximal and distal sites cooling from 34 to 22 degrees C caused more than a twofold increase in the duration of hyperpolarization and time to peak depolarization. However, the increase in the absolute time of the duration of hyperpolarization and the time to peak depolarization was significantly greater at the distal than proximal esophageal site. Cooling to 16 degrees C decreased RMP and nearly abolished the biphasic membrane potential response.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals Effect of acetylcholine on postjunctional membrane permeability in eel electroplaque.

1977 ◽  
Vol 70 (1) ◽  
pp. 23-36 ◽  
Author(s):  
N L Lassignal ◽  
A R Martin
Keyword(s):  
Field Equation ◽  
Membrane Potential ◽  
Membrane Permeability ◽  
Ionic Composition ◽  
Reversal Potential ◽  
Resting Potential ◽  
Constant Field ◽  
Free Solution ◽  
Positive Direction ◽  
External K

Acetylcholine (ACh) was applied iontophoretically to the innervated face of isolated eel electroplaques while the membrane potential was being recorded intracellularly. At the resting potential (about -85 mV) application of the drug produced depolarizations (ACh potentials) of 20 mV or more which became smaller when the membrane was depolarized and reversed in polarity at about zero membrane potential. The reversal potential shifted in the negative direction when external Na+ was partially replaced by glucosamine. Increasing external K+ caused a shift of reversal potential in the positive direction. It was concluded that ACh increased the permeability of the postjunctional membrane to both ions. Replacement of Cl- by propionate had no effect on the reversal potential. In Na+-free solution containing glucosamine the reversal potential was positive to the resting potential, suggesting that ACh increased the permeability to glucosamine. Addition of Ca++ resulted in a still more positive reversal potential, indicating an increased permeability to Ca++ as well. Analysis of the results indicated that the increases in permeability of the postjunctional membrane to K+, Na+, Ca++, and glucosamine were in the ratios of approximately 1.0:0.9:0.7:0.2, respectively. With these permeability ratios, all of the observed shifts in reversal potential with changes in external ionic composition were predicted accurately by the constant field equation.

scholarly journals Mechanism of depolarization of rat cortical synaptosomes at submicromolar external Ca2+ activity. The use of Ca2+ buffers to control the synaptosomal membrane potential

1985 ◽  
Vol 225 (3) ◽  
pp. 671-680 ◽  
Author(s):  
G Schmalzing
Keyword(s):  
Plasma Membrane ◽  
Field Equation ◽  
Membrane Potential ◽  
Ruthenium Red ◽  
Membrane Potentials ◽  
Constant Field ◽  
Permeability Ratio ◽  
Rapid Fall ◽  
Sucrose Medium ◽  
Micromolar Range

Rat cortical synaptosomes responded to a reduction of external Ca2+ from pCa 3.5 to pCa 4.8 in the absence of MgCl2 with a slight decrease of internal K+ and an increase of Na+. The effects were prevented by tetrodotoxin or millimolar concentrations of MgCl2. Further lowering of external pCa to 7.7 with N-hydroxyethylethylenediaminetriacetate evoked a rapid fall of internal K+, which was specifically blocked by Ruthenium Red; tetrodotoxin and nifedipine were ineffective. A linear relationship was established between K+ and methyltriphenylphosphonium cation distribution ratios by varying external pCa between 4.8 and 7.7, indicating that K+ efflux resulted from a depolarization of the plasma membrane. An increase of Na+ permeability was suggested by the synaptosomes' gain of Na+ and the disappearance of the depolarization in an Na+-free sucrose medium. According to the constant field equation, the permeability ratio PNa/PK increased from 0.029 at pCa4.8 to 0.090 at pCa 7.7 with plasma membrane potentials of −74mV and −47mV, respectively. Since the plasma membrane responded to variation of external Ca2+ activities in the micromolar range with a graded and sustained depolarization, the use of Ca2+ buffers to control membrane potentials is suggested.

scholarly journals Ionic Relations of Cells of Ohara Australis R.BR. IV. Membrane Potential Differences and Resistances

1961 ◽  
Vol 14 (1) ◽  
pp. 26 ◽  
Author(s):  
AB Hope ◽  
NA Walker
Keyword(s):  
Cell Wall ◽  
Field Equation ◽  
Membrane Potential ◽  
Cytoplasmic Membrane ◽  
External Medium ◽  
Voltage Characteristic ◽  
Potential Difference ◽  
Constant Field ◽  
Sodium Ions ◽  
Ionic Relations

Experiments are described in which the electric potential difference and resistance between the cytoplasm and the external medium were measured in cells of Ohara australi8. The method was designed to eliminate the effect of the negatively charged Donnan system of the cell wall. Both the potential difference and the resistance are attributed to the outer cytoplasmic membrane. It is shown that they may be quantitatively explained by the passive diffusion of potassium and sodium ions across the membrane with permeabilities of the order of 10-5 and 10-8 cm sec-1 respectively. The resistance-voltage characteristic of the membrane is accurately predicted by the constant field equation of Goldman (1943). The ignificance of these findings is discussed.

scholarly journals SLO2.1 and NALCN form a functional complex to modulate myometrial cell excitability

2020 ◽  
Author(s):  
Juan J. Ferreira ◽  
Chinwendu Amazu ◽  
Lis C. Puga-Molina ◽  
Sarah K. England ◽  
Celia M. Santi
Keyword(s):  
Membrane Potential ◽  
Resting Membrane Potential ◽  
Quiescent State ◽  
Leak Current ◽  
Contractile State ◽  
Cell Excitability ◽  
Leak Channel ◽  
Functional Complex ◽  
Myometrial Smooth Muscle Cell ◽  
Myometrial Contractility

AbstractAt the end of pregnancy, the uterus transitions from a quiescent state to an excitable, contractile state. These changes are linked to depolarization of the myometrial smooth muscle cell (MSMC) resting membrane potential. The membrane potential is primarily determined by the balance between an outward potassium (K+) leak current and an inward sodium (Na+) leak current. We recently described a Na+-activated K+ channel (SLO2.1) and a non-selective Na+ leak channel (NALCN) in human MSMCs. Here, we asked whether these channels function together. We show that SLO2.1 currents are activated by an inward NALCN-dependent Na+ leak current, leading to MSMC hyperpolarization. The regulation of the membrane potential by NALCN/SLO2.1 activity modulates both Ca2+ entry through VDCCs, and myometrial contractility. Finally, NALCN and SLO2.1 are in proximity to one another in human MSMCs. We conclude that SLO2.1 and NALCN function together to regulate human MSMC membrane potential and excitability.

scholarly journals Current- and Voltage-Clamped Studies on Myxicola Giant Axons

1969 ◽  
Vol 54 (6) ◽  
pp. 730-740 ◽  
Author(s):  
L. Binstock ◽  
L. Goldman
Keyword(s):  
Steady State ◽  
Membrane Potential ◽  
Action Potential ◽  
Voltage Clamp ◽  
Transient Current ◽  
Resting Membrane Potential ◽  
Action Potential Amplitude ◽  
Giant Axons ◽  
Potential Amplitude ◽  
Steady State Current

A new dissection procedure for preparing Myxicola giant axons for observation under voltage clamp is described. Preparation time is generally 40–45 min. 65–70% of the preparations attempted may be brought through the entire procedure, including insertion of the long internal electrode, and support an initial action potential amplitude of 100 mv or greater. Mean values for axon diameter, resting membrane potential, action potential amplitude, maximum peak inward transient current, and resting membrane resistance are 560 µ, —66.5 mv, 112 mv, 0.87 ma/cm2 and 1.22 KΩ cm 2 respectively. Cut branches do not seem to be a problem in this preparation. Behavior under voltage clamp is reasonably stable over several hours. Reductions in maximum inward transient current of 10% and in steady-state current of 5–10% are expected in the absence of any particular treatment. Tetrodotoxin blocks the action potential and both the inward and outward transient current, but has no effect on either the resting membrane potential or the steady-state current. This selective action of tetrodotoxin on the transient current is taken as an indication that this current component is probably carried by Na.

Endurance training alters outward K+current characteristics in rat cardiocytes

2001 ◽  
Vol 90 (4) ◽  
pp. 1327-1333 ◽  
Author(s):  
Korinne N. Jew ◽  
M. Charlotte Olsson ◽  
Eric A. Mokelke ◽  
Bradley M. Palmer ◽  
Russell L. Moore
Keyword(s):  
Membrane Potential ◽  
Action Potential ◽  
Primary Culture ◽  
Left Ventricular ◽  
Resting Membrane Potential ◽  
Sprague Dawley ◽  
Whole Cell ◽  
Time To Peak ◽  
Time Required ◽  
In Cells

The effect of endurance run training on outward K+ currents with rapidly inactivating ( I to) and sustained or slowly inactivating ( I sus) characteristics was examined in left ventricular (LV) cardiocytes isolated from sedentary (Sed) and treadmill-trained (Tr) female Sprague-Dawley rats. Isolated LV cardiocytes were used in whole cell patch-clamp studies to characterize whole cell I to and I sus. Peak I to was greatest in cells isolated from the Tr group. When I to was corrected for cell capacitance to yield a current density, most, but not all, of the Sed vs. Tr differences in I to magnitude were eliminated. Regardless of how I to was expressed (e.g., I to or I todensity), the time required to achieve a peak value was markedly shortened in the cardiocytes isolated from the Tr group. Training elicited a reduction in I sus density. Action potential characteristics were determined in Sed and Tr cardiocytes in primary culture. Training did not affect resting membrane potential, whereas peak membrane potential was reduced and time to peak membrane potential was prolonged in the Tr group. In addition, time to 50% repolarization was significantly increased in cells from the Tr group. Collectively, these data indicate that I to and I sus characteristics are altered by training in isolated LV cardiocytes. These alterations in I to and I sus may be responsible, at least in part, for the training-induced alterations in action potential configuration in cardiocytes in primary culture.

scholarly journals Current Separations in Myxicola Giant Axons

1969 ◽  
Vol 54 (6) ◽  
pp. 741-754 ◽  
Author(s):  
L. Goldman ◽  
L. Binstock
Keyword(s):  
Membrane Potential ◽  
Action Potential ◽  
Reversal Potential ◽  
Transient Current ◽  
Resting Potential ◽  
Equilibrium Potential ◽  
Resting Membrane Potential ◽  
Concentration Data ◽  
Giant Axons ◽  
Current Reversal

The effect of reducing the external sodium concentration, [Na]o, on resting potential, action potential, membrane current, and transient current reversal potential in Myxicola giant axons was studied. Tris chloride was used as a substitute for NaCl. Preliminary experiments were carried out to insure that the effect of Tris substitution could be attributed entirely to the reduction in [Na]o. Both choline and tetramethylammonium chloride were found to have additional effects on the membrane. The transient current is carried largely by Na, while the delayed current seems to be independent of [Na]o. Transient current reversal potential behaves much like a pure Nernst equilibrium potential for sodium. Small deviations from this behavior are consistent with the possibility of some small nonsodium component in the transient current. An exact PNa/PK for the transient current channels could not be computed from these data, but is certainly well greater than unity and possibly quite large. The peak of the action potential varied with [Na]o as expected for a sodium action potential with some substantial potassium permeability at the time of peak. Resting membrane potential is independent of [Na]o. This finding is inconsistent with the view that the resting membrane potential is determined only by the distribution of K and Na, and PNa/PK. It is suggested that PNa/PK's obtained from resting membrane potential-potassium concentration data do not always have the physical meaning generally attributed to them.

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