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.

An Investigation of the Electrogenic Sodium Pump in Snail Neurones, Using the Constant-Field Theory

1969 ◽  
Vol 51 (1) ◽  
pp. 181-201
Author(s):  
R. B. MORETON
Keyword(s):  
Field Equation ◽  
Sodium Pump ◽  
Membrane Resistance ◽  
Resting Potential ◽  
Constant Field ◽  
Sodium Ions ◽  
Intracellular Potassium ◽  
Electrogenic Sodium Pump ◽  
Snail Neurones ◽  
Intracellular Potassium Concentration

1. Sodium ions injected into giant neurones of Helix aspersa by diffusion from low-resistance microelectrodes caused hyperpolarization of the cells. Under these conditions the behaviour of the resting potential could be described by a modified ‘constant-field’ equation, including a term representing the effect of a potassiumsensitive, electrogenic sodium pump. 2. Exposure to potassium-free solution, ouabain or cyanide abolished the hyperpolarization, and caused a gradual fall in the intracellular potassium concentration, as estimated from the constant-field equation. 3. Assuming that this fall was due to replacement of intracellular potassium by injected sodium ions, it was possible to calculate the rates of injection and pumping of sodium ions, and, using the measured membrane resistance of the cell, the hyperpolarization which the sodium pump could cause, if it were electrogenic. 4. This was related to the observed hyperpolarization, supporting the view that the latter was caused by stimulation of the electrogenic sodium pump.

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 Chara Australls X. Effects of Bicarbonate Ions on Electrical Properties

1965 ◽  
Vol 18 (4) ◽  
pp. 789 ◽  
Author(s):  
AB Hope
Keyword(s):  
Electrical Properties ◽  
External Medium ◽  
Membrane Resistance ◽  
Potential Difference ◽  
Bicarbonate Ions ◽  
Ionic Relations

When bicarbonate ions were added to the external medium the plasmalemma of cells of Ohwra australis became hyperpolarized. The potential difference (p.d.) frequently changed from -150 or -160 mY to -200 or -220 mY. An increal!El in membrane resistance also occurred.

scholarly journals K-Na Discrimination by Porous Filters Saturated with Organic Solvents As Expressed by Diffusion Potentials

1963 ◽  
Vol 46 (4) ◽  
pp. 839-850 ◽  
Author(s):  
A. Ilani
Keyword(s):  
Field Equation ◽  
Organic Solvents ◽  
Potential Difference ◽  
Constant Field ◽  
Concentration Gradients ◽  
Permeability Ratio ◽  
Inverse Proportion ◽  
Diffusion Potentials ◽  
Millipore Filters ◽  
Butanol Solution

The permeability ratio of Millipore filters saturated with organic solvents to K and to Na has been studied by measuring the potential difference across these filters. It was found that with n-octanol, toluene, and chloroform the membranes were more permeable to K+ than to Na+, the degree of discrimination being in inverse proportion to the polarity of the solvent. The dependence of NaCl and KCl diffusion potentials upon the concentration gradients across a filter soaked with about 1:1 toluene/n-butanol solution, could be expressed by the constant field equation, if it is assumed that this layer is 6 to 7 times more permeable to K+ than to Na+ and that the permeability to Cl- is negligible. Elevating the fraction of toluene in n-butanol in the separating phase makes it more selective.

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.

scholarly journals Active Transport of Potassium by the Giant Neuron of the Aplysia Abdominal Ganglion

1972 ◽  
Vol 60 (5) ◽  
pp. 519-533 ◽  
Author(s):  
J. M. Russell ◽  
A. M. Brown
Keyword(s):  
Field Equation ◽  
Membrane Potential ◽  
Active Transport ◽  
Aplysia Californica ◽  
Constant Field ◽  
Electrochemical Gradient ◽  
Nernst Equation ◽  
Giant Neuron ◽  
Potassium Flux ◽  
External Potassium

We measured the internal potassium activity, aiK, and membrane potential, Em, simultaneously in 111 R2 giant neurons of Aplysia californica. aiK was 165.3 ± 3.4 mM, Em was -47.8 ± 0.9 mv, and EK calculated using the Nernst equation was -76.9 ± 0.05 mv. Such values were maintained for as long as 6 hr of continuous recording in untreated cells, aiK fell exponentially after the following treatments: cooling to 0.5°–4°C, ouabain, zero external potassium, 2,4-dinitrophenol, and cyanide. The effects of cooling and zero potassium were reversible. Potassium permeability was calculated from net potassium flux using the constant field equation and ranged from 2.6 to 18.5 x 10-8 cm/sec. We conclude that potassium is actively transported into this neuron against a 30–40 mv electrochemical gradient.

Membrane potential differences in Chara australis

1962 ◽  
Vol 156 (965) ◽  
pp. 573-577 ◽  
Keyword(s):  
Membrane Potential ◽  
Electric Potential ◽  
Sodium Pump ◽  
External Medium ◽  
Ionic Composition ◽  
Passive Diffusion ◽  
Potential Difference ◽  
Potassium Sodium ◽  
Electric Potential Difference ◽  
Chara Australis

The observations of Hope & Walker (1961) on the electric potential difference between the cytoplasm of cells of Chara australis and the external medium, when the ionic composition of the latter was varied, are considered in relation to a chloride, or sodium, pump with passive diffusion of potassium, sodium and chloride. The observations agree, atleast, as well with such a system as they do with the system suggested by Hope & Walker, which is restricted to passive diffusion of potassium and sodium.

Sensitivity of normal and mutant strains of Escherichia coli to actinomycin-D

1972 ◽  
Vol 18 (6) ◽  
pp. 909-915 ◽  
Author(s):  
A. P. Singh ◽  
K.-J. Cheng ◽  
J. W. Costerton ◽  
E. S. Idziak ◽  
J. M. Ingram
Keyword(s):  
Escherichia Coli ◽  
Cell Wall ◽  
Wild Type Strain ◽  
Actinomycin D ◽  
Cytoplasmic Membrane ◽  
Cell Envelope ◽  
Coli Strain ◽  
Wild Type ◽  
Mutant Strains ◽  
In The Wild

The site of the cell barrier to actinomycin-D uptake was studied using a wild-type Escherichia coli strain P and its cell envelope-defective filamentous mutants, strains 6γ and 12γ, both of which 'leak' β-galactosidase and alkaline phosphatase into the medium during growth indicating both membrane and cell-wall defects. Actinomycin-D entered the cells of these two mutant strains as evidenced by the inhibition of both 14C-uracil incorporation and synthesis of the induced β-galactosidase system. Under similar conditions, no inhibition occurred in the wild-type strain and its sucrose-lysozyme prepared spheroplasts. Actinomycin-D did, however, inhibit the above-mentioned systems in the wild-type sucrose-lysozyme spheroplasts prepared in the presence of 2 mM EDTA. The experimental data indicate that although the cell wall may act as a primary barrier or sieve to actinomycin-D, the cytoplasmic membrane should be considered the final and determinative barrier to this antibiotic.

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