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.

Membrane Potentials in Amoeba Proteus

1966 ◽  
Vol 45 (2) ◽  
pp. 251-267
Author(s):  
M. S. BINGLEY
Keyword(s):  
Plasma Membrane ◽  
Membrane Potential ◽  
Morphological Changes ◽  
Amoeba Proteus ◽  
Membrane Potentials ◽  
The Other ◽  
The Earth ◽  
Electrode Resistance ◽  
Alternating Voltage

1. Amoebae can be penetrated by microelectrodes at either end. One records voltage and the other supplies alternating current. 2. Step-like increases in alternating voltage superimposed on potentials recorded by the voltage electrode when in either the pseudopod or rear region demonstrate that low potentials recorded from a pseudopod and high ones from the rear region exist across a discrete impedance barrier. The only structure so far shown to fulfil this function is the plasma membrane. 3. A resistance inserted in the earth path monitors current flowing through the system and confirms observations made when recording with single electrodes that there is a reduction of electrode resistance when the cell is entered. 4. Pronounced depolarization in the rear region is shown when the current-carrying electrode penetrates the pseudopod, but not vice versa. 5. Morphological changes associated with membrane potential reversal are illustrated. 6. Consideration is given to the role of step-like potential changes in movement.

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 Energy transduction in intact synaptosomes. Influence of plasma-membrane depolarization on the respiration and membrane potential of internal mitochondria determined in situ

1980 ◽  
Vol 186 (1) ◽  
pp. 21-33 ◽  
Author(s):  
I D Scott ◽  
D G Nicholls
Keyword(s):  
Plasma Membrane ◽  
Membrane Potential ◽  
Mitochondrial Membrane Potential ◽  
Mitochondrial Membrane ◽  
Significant Proportion ◽  
Membrane Potentials ◽  
Simultaneous Estimation ◽  
Anaerobic Glycolysis ◽  
Mitochondrial Potential ◽  
Plasma Membrane Potential

A method is described, based on the differential accumulation of Rb+ and methyltriphenylphosphonium, for the simultaneous estimation of the membrane potentials across the plasma membrane of isolated nerve endings (synaptosomes), and across the inner membrane of mitochondria within the synaptosomal cytoplasm. These determinations, together with measurements of respiratory rates, and ATP and phosphocreatine concentrations, are used to define the bioenergetic behaviour of isolated synaptosomes under a variety of conditions. Under control conditions, in the presence of glucose, the plasma and mitochondrial membrane potentials are respectively 45 and 148mV. Addition of a proton translocator induces a 5-fold increase in respiration, and abolishes the mitochondrial membrane potential. The addition of rotenone to inhibit respiration does not affect the plasma membrane potential, and only lowers the mitochondrial membrane potential to 128mV. Evidence is presented that ATP synthesis by anaerobic glycolysis is sufficient under these conditions to maintain ATP-dependent processes, including the reversal of the mitochondrial ATP synthetase. Addition of oligomycin under non-respiring conditions leads to a complete collapse of the mitochondrial potential. Even under control conditions the plasma membrane (Na+ + K+)-dependent ATPase is responsible for a significant proportion of the synaptosomal ATP turnover. Veratridine greatly increases respiration, and depolarizes the plasma membrane, but only slightly lowers the mitochondrial membrane potential. High K+ and ouabain also lower the plasma membrane potential without decreasing the mitochondrial membrane potential. In non-respiring synaptosomes, anaerobic glycolysis is incapable of maintaining cytosolic ATP during the increased turnover induced by veratridine, and the mitochondrial membrane potential collapses. It is concluded that the internal mitochondria must be considered in any study of synaptosomal transport.

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 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.

Extracellularly applied ruthenium red and cADP ribose elevate cytosolic Ca2+ in isolated rat osteoclasts

1996 ◽  
Vol 270 (3) ◽  
pp. F469-F475 ◽  
Author(s):  
O. A. Adebanjo ◽  
V. S. Shankar ◽  
M. Pazianas ◽  
B. J. Simon ◽  
F. A. Lai ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Membrane Potential ◽  
Cell Membrane ◽  
Cell Surface ◽  
Divalent Cation ◽  
Ruthenium Red ◽  
The Face ◽  
A Cell ◽  
Cation Sensing ◽  
Isolated Rat

We demonstrated recently that the divalent cation-sensing receptor on the osteoclast, the Ca2+ receptor (CaR), is a functional component of a cell surface-expressed ryanodine receptor-like molecule (RyR). The objective of the present study was to further characterize this putative RyR by use of the two well-known cell-impermeant RyR modulators, ruthenium red and adenosine 3',5'-cyclic diphosphate ribose (cADPr). We found that, when applied extracellularly, ruthenium red (5 x 10(-8)-10(-4) M) and cADPr (5 x 10(-6) M) triggered an elevation of cytosolic [Ca2+]. Depolarization of the cell membrane by the application of 0.1 M K+ in the presence of 5 x 10(-6) M. valinomycin resulted in a concentration-dependent increase in the magnitude of the cytosolic Ca2+ response to extracellular ruthenium red (5 x 10(-9) and 5 x 10(-5) M), a phenomenon that was not seen when osteoclasts were hyperpolarized using 5 x 10(-3) M K+ with 5 x 10(-6) M valinomycin. In the presence of an intact nonleaky cell membrane, these results would favor a plasma membrane locus of action for the two modulators. Furthermore, pretreatment of osteoclasts with either modulator resulted in a markedly attenuated cytosolic Ca2+ transient elicited in response to the CaR agonist Ni2+, thus confirming an interaction between the cADPr- and ruthenium red-sensitive sites and the osteoclast CaR. The inhibition of the cytosolic Ca2+ response to Ni2+ induced by ruthenium red remained unchanged in the face of membrane potential changes. Finally, the cytosolic Ca2+ response to caffeine (5 x 10(-4) M), another RyR modulator, was also strongly attenuated by pretreatment with 5 x 10(-9) M ruthenium red. We conclude that ruthenium red and cADPr act on plasma membrane-resident sites and that both these sites interact with the process of divalent cation sensing.

scholarly journals CHANGING ELECTRICAL CONSTANTS OF THE FUNDULUS EGG PLASMA MEMBRANE

1956 ◽  
Vol 40 (1) ◽  
pp. 107-119 ◽  
Author(s):  
C. Y. Kao
Keyword(s):  
Plasma Membrane ◽  
Membrane Potential ◽  
Pore Size ◽  
Sucrose Solution ◽  
Membrane Resistance ◽  
Transient Method ◽  
Membrane Capacity ◽  
Rapid Fall ◽  
Activated State ◽  
Effective Pore Size

Electrical constants of the plasma membrane of the Fundulus egg have been measured with microelectrodes by the transient method. No consistent and significant membrane potential was measured. Membrane capacity averages 0.63 µF/cm.2 for both unactivated and activated eggs. Membrane resistance averages 3450 ohm-cm.2 in the unactivated eggs, but increases 2 to 7 times to an average of 13,290 ohm-cm.2 in the fully activated state. In a hypertonic sucrose solution, the swelling of the egg proper is accompanied by a rapid fall of membrane resistance towards that in the unactivated state. The changes of the membrane resistance are interpreted as probably caused by alterations in the effective pore size in the plasma membrane.

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