scholarly journals Electrogenic Ion Pump in Plants-A Review

1975 ◽  
Vol 15 (3) ◽  
pp. 113-124 ◽  
Author(s):  
Hisashi OKAMOTO
Keyword(s):  
Ion Pump ◽  
Electrogenic Ion Pump

Amiloride-Sensitive Sodium Flux and Potentials in Perfused Carcinus Gill: Preparations

1986 ◽  
Vol 122 (1) ◽  
pp. 25-35
Author(s):  
ČEDOMIL LUCU ◽  
DIETRICH SIEBERS
Keyword(s):  
External Solution ◽  
Inhibitory Effect ◽  
Control Group ◽  
Ion Pump ◽  
Maximal Inhibition ◽  
Leaky Epithelia ◽  
Perfusion Solution ◽  
Sodium Flux ◽  
Gill Filaments ◽  
Electrogenic Ion Pump

Sodium and chloride fluxes, as well as transbranchial potentials (TBP) were studied in isolated perfused gill filaments of the crab Carcinus mediterraneus. Experiments were carried out in media that were either hyposmotic to the perfusion solution (asymmetrical conditions) or isosmotic (symmetrical conditions). Fluxes were found to be diffusional in gills under asymmetrical conditions; amiloride induced an inhibitory effect on influxes, without affecting TBP. Under symmetrical conditions, TBP was −7.6±2.3mV, suggesting that the electrogenic ion pump contributes significantly to the development of TBP. Immediately after addition of 2.5 × 10−4 moll−1 amiloride to the external solution, sodium influxes were reduced to 31% of those in the control group, and TBP was significantly hyperpolarized from −7.6 to −14.8 mV. The absence of Ca2+ under symmetrical conditions diminished TBP hyperpolarization. Half-maximal inhibition of sodium influxes by amiloride was at 7 × 10−5 moll−1. This low amiloride affinity is typical of low resistance leaky epithelia. Sodium transport is discussed as an amiloride-affected influx, probably as a Na/H antiport.

scholarly journals Origin of the membrane potential in plasmodial droplets of Physarum polycephalum. Evidence for an electrogenic pump.

1981 ◽  
Vol 78 (6) ◽  
pp. 637-655 ◽  
Author(s):  
H Kuroda ◽  
R Kuroda
Keyword(s):  
Membrane Potential ◽  
Potassium Cyanide ◽  
Equilibrium Potential ◽  
Ion Pump ◽  
Electrophysiological Studies ◽  
Concentration Changes ◽  
Electrogenic Ion Pump ◽  
Ph Range ◽  
Physarum Plasmodia ◽  
Spherical Droplets

Spherical droplets, derived from Physarum plasmodia by incubation in 10 mM caffeine, seemed to be an excellent system for electrophysiological studies because they were large (less than or equal to 300 micrometer in diameter) and because they tolerated intracellular electrodes filled with 3 M KCl and 10 mM EDTA for a few hours. Intact plasmodia, by contrast, gave valid records for only a few minutes. Under standard conditions ([K+]o = 1 mM, [Na+]o = 5 mM, [Ca++]0 = 0.5 mM, [Mg++]o = 2 mM, and [Cl-]o = 6 mM at pH 7.0), the potential difference across droplet membranes was -80 to -120mV, interior negative. The membrane potential was only slightly sensitive to concentration changes for the above-mentioned ions, and was far negative to the equilibrium diffusion potentials calculated from the known internal contents of K, Na, Ca, Mg, and CL (29.4, 1.6, 3.7, 6.5, and 27.8 mmol/kg, respectively). Variations of external pH did have a strong influence on the membrane potential, yielding a slope of 59 mV/pH between pH 6.5 and 5.5. In this pH range, however, the equilibrium potential for H+ (assuming 6.2 less than or equal to pHi less than or equal to 7.0) was greater than 75 mV positive to the observed membrane potential. Membrane potential was directly responsive to metabolic events, being lowered by potassium cyanide, and by cooling from 25 to 12 degrees C. This ensemble of results strongly indicates that the major component of membrane potential in plasmodial droplets of Physarum is generated by an electrogenic ion pump, probably one extruding H+ ions.

scholarly journals Effects of Some Inhibitors on the Temperature-Dependent Component of Resting Potential in Lobster Axon

1967 ◽  
Vol 50 (7) ◽  
pp. 1835-1848 ◽  
Author(s):  
Joseph P. Senft
Keyword(s):  
Membrane Potential ◽  
Electrode Potential ◽  
Potassium Ion ◽  
Potential Change ◽  
Resting Potential ◽  
Resting Membrane Potential ◽  
Ion Pump ◽  
Perfusion Medium ◽  
Axon Membrane ◽  
Electrogenic Ion Pump

The resting membrane potential of the lobster axon becomes 5–8 mv more negative when the temperature of the perfusion solution is increased 10°C. This potential change is about twice that predicted if the axon membrane potential followed that expected for a potassium ion electrode potential. When the inhibitors, 2, 4-dinitrophenol, sodium cyanide, and sodium azide, were added separately to the perfusion medium the potential change was reduced to about 1.4 times that predicted for a potassium ion electrode potential. Assays of axons exposed to these inhibitors showed that ATP levels were reduced to about one-fourth that obtained for control axons. Ouabain added to the perfusion medium reduced the potential change to that expected for a potassium ion electrode potential. These results suggest that the resting potential changes with temperature as a result of the activity of an electrogenic ion pump.

Active ion transport and resting potential in smooth muscle cells

1973 ◽  
Vol 265 (867) ◽  
pp. 47-56 ◽  
Keyword(s):  
Membrane Potential ◽  
Membrane Resistance ◽  
Resting Potential ◽  
Ion Pump ◽  
Experimental Procedure ◽  
Ion Concentrations ◽  
Maximal Activation ◽  
Active Ion Transport ◽  
Membrane Permeabilities ◽  
Electrogenic Ion Pump

The diffusion potential in taenia coli cells calculated from the intra- and extracellular ion concentrations and from the calculated membrane permeabilities is less negative than the measured membrane potential. This discrepancy could be due to a continuous contribution of an electrogenic ion pump to the membrane potential. This hypothesis is supported by the finding that the sum of the active ion fluxes is sufficiently large to generate a potential of — 20 mV across the membrane. Moreover, an unequivocal electrogenic component of the membrane potential has been demonstrated during maximal activation of the ion pump in K-depleted cells. The importance of this electrogenic component depends on the membrane resistance, a parameter which is very much affected by the experimental procedure. The active Na-K exchange is stimulated by [Na] 1 , and [K] 0 and is inhibited by [Na] 0 . Furthermore, it has been observed that 47% of the Na-exchange of Na-enriched tissues is due to Na exchange diffusion.

scholarly journals Electrophysiological properties of Achlya hyphae: ionic currents studied by intracellular potential recording.

1986 ◽  
Vol 102 (4) ◽  
pp. 1209-1216 ◽  
Author(s):  
D L Kropf
Keyword(s):  
Membrane Potential ◽  
Ionic Currents ◽  
Internal Field ◽  
Defined Medium ◽  
Ion Pump ◽  
Hyphal Length ◽  
Electrophysiological Properties ◽  
Inorganic Ion ◽  
Electrogenic Ion Pump ◽  
Ph Range

The electrical properties of the water mold Achlya bisexualis were investigated using intracellular microelectrodes. Hyphae growing in a defined medium maintained a membrane potential (Vm) of -150 to -170 mV, interior negative. Under the conditions used here, this potential was insensitive to changes in the inorganic ion composition of the medium. Changes in external pH did affect Vm, but only outside the physiological pH range. By contrast, the addition of respiratory inhibitors caused a rapid depolarization without affecting the conductance of the plasma membrane. Taken together these findings strongly suggest that the membrane potential is governed by an electrogenic ion pump rather than by an ionic diffusion potential. Previous work from this laboratory showed that Achlya hyphae generate a transcellular proton current that enters the growing tip, flows along the hyphal length, and exits distally from the trunk. These initial experiments used an extracellular vibrating electrode, and I now report intracellular electrical recordings which support the hypothesis that protons enter the tip by symport with amino acids and are expelled distally by a proton-translocating ATPase. Most significantly, current flowing intracellularly along the hyphal length is associated with a cytoplasmic electric field of 0.2 V/cm or greater. Conditions that inhibit the current also abolish the internal field, suggesting that these two phenomena are closely linked.

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