scholarly journals The influence of external cations and membrane potential on Ca-activated Na efflux in Myxicola giant axons.

1978 ◽  
Vol 71 (4) ◽  
pp. 453-466 ◽  
Author(s):  
R A Sjodin ◽  
R F Abercrombie
Keyword(s):  
Membrane Potential ◽  
Direct Action ◽  
Monovalent Cation ◽  
Coupling Ratio ◽  
Large Component ◽  
Experimental Conditions ◽  
Giant Axons ◽  
Threefold Increase ◽  
Na Efflux ◽  
External K

In microinjected Myxicola giant axons with elevated [Na]i, Na efflux was sensitive to Cao under some conditions. In Li seawater, sensitivity to Cao was high whereas in Na seawater, sensitivity to Cao was observed only upon elevation of [Ca]o above the normal value. In choline seawater, the sensitivity of Na efflux to Cao was less than that observed in Li seawater whereas Mg seawater failed to support any detectable Cao-sensitive Na efflux. Addition of Na to Li seawater was inhibitory to Cao-sensitive Na efflux, the extent of inhibition increasing with rising values of [Na]o. The presence of 20 mM K in Li seawater resulted in about a threefold increase in the Cao-activated Na efflux. Experiments in which the membrane potential, Vm, was varied or held constant when [K]o was changed showed that the augmentation of Ca-activated Na efflux by Ko was not due to changes in Vm but resulted from a direct action of K on activation by Ca. The same experimental conditions that favored a large component of Cao-activated Na efflux also caused a large increase in Ca influx. Measurements of Ca influx in the presence of 20 mM K and comparison with values of Ca-activated Na efflux suggest that the Na:Ca coupling ratio may be altered by increasing external [K]o. Overall, the results suggest that the Cao-activated Na efflux in Myxicola giant axons requires the presence of an external monovalent cation and that the order of effectiveness at a total monovalent cation concentration of 430 mM is K + Li greater than Li greater than Choline greater than Na.

scholarly journals Strophanthidin-sensitive sodium fluxes in metabolically poisoned frog skeletal muscle.

1976 ◽  
Vol 68 (4) ◽  
pp. 405-420 ◽  
Author(s):  
B G Kennedy ◽  
P De Weer
Keyword(s):  
Skeletal Muscle ◽  
Membrane Potential ◽  
Human Erythrocyte ◽  
Sodium Pump ◽  
Giant Axon ◽  
Squid Giant Axon ◽  
Frog Skeletal Muscle ◽  
Na Efflux ◽  
Unidirectional Fluxes ◽  
External K

Strophanthidin-sensitive and insensitive unidirectional fluxes of Na were measured in fog sartorius muscles whose internal Na levels were elevated by overnight storage in the cold. ATP levels were lowered, and ADP levels raised, by metabolic poisoning with either 2,4-dinitrofluorobenzene or iodoacetamide. Strophanthidin-sensitive Na efflux and influx both increased after poisoning, while strophanthidin-insensitives fluxes did not. The increase in efflux did not require the presence of external K but was greatly attenuated when Li replaced Na as the major external cation. Membrane potential was not markedly altered by 2,4-dinitrofluorobenzene. These observations indicate that the sodium pump of frog skeletal muscle resembles that of squid giant axon and human erythrocyte in its ability to catalyze Na-Na exchange to an extent determined by intracellular ATP/ADP levels.

Nombres de Transport, tK, tNa et tca Pour la Membrane de la Cellule Hépatique In Vivo

1972 ◽  
Vol 50 (5) ◽  
pp. 416-422 ◽  
Author(s):  
Jean Pierre Caillé ◽  
O. F. Schanne
Keyword(s):  
Membrane Potential ◽  
Liver Cell ◽  
Ionic Mobility ◽  
Irreversible Thermodynamics ◽  
Transport Numbers ◽  
Experimental Conditions ◽  
External Potassium ◽  
K Concentration ◽  
External K

We measured the membrane potential of the liver cell in vivo at 38 °C as we increased the external potassium. For the range of K concentration from 20.4 to 78 mM, the membrane potential of the liver cell decreased with a slope of 20.2 mV per decade change in external K concentration. The tissue content of K, Na, and Cl was analyzed under the same experimental conditions. The cytoplasmic resistivity (111 ± 17.5 Ω-cm) was used as a criterion for the state of the ions in the cytoplasm. This result, when it is compared with the value predicted from the ionic content, suggests that either the ionic mobility or the ionic activity in the cytoplasm of the liver cell is less than in a simple salt solution. An analytical expression, derived with the use of irreversible thermodynamics, permits us to calculate the transport numbers for the ions K, Na, and Cl in the membrane of the liver cell (tK 0.28, tNa 0.12, tCl 0.61).

scholarly journals The Influence of Sodium-Free Solutions on the Membrane Potential of Frog Muscle Fibers

1963 ◽  
Vol 47 (1) ◽  
pp. 117-132 ◽  
Author(s):  
L. J. Mullins ◽  
K. Noda
Keyword(s):  
Membrane Potential ◽  
Activity Coefficients ◽  
Muscle Fibers ◽  
Frog Muscle ◽  
Sartorius Muscle ◽  
Coupling Ratio ◽  
Nernst Equation ◽  
Ringer’S Solution ◽  
Na Efflux ◽  
Frog Sartorius

The membrane potential of frog sartorius muscle fibers in a Cl- and Na-free Ringer's solution when sucrose replaces NaCl is about the same as that in normal Ringer's solution. The K+ efflux is also about the same in the two solutions but muscles lose K and PO4 in sucrose Ringer's solutions. The membrane potential in sucrose Ringer's solution is equal to that given by the Nernst equation for a K+ electrode, when corrections are made for the activity coefficients for K+ inside and outside the fiber. For a muscle in normal Ringer's solution, the measured membrane potential is within a few millivolts of EK. This finding is incompatible with a 1:1 coupled Na-K pump. It is consistent with either no coupling of Na efflux to K influx, or a coupling ratio of 3 or greater.

scholarly journals Fast Inactivation of Delayed Rectifier K Conductance in Squid Giant Axon and Its Cell Bodies

1997 ◽  
Vol 109 (4) ◽  
pp. 435-448 ◽  
Author(s):  
Chris Mathes ◽  
Joshua J.C. Rosenthal ◽  
Clay M. Armstrong ◽  
William F. Gilly
Keyword(s):  
Large Fraction ◽  
Giant Axon ◽  
Delayed Rectifier ◽  
Inactivation Kinetics ◽  
Temperature Sensitive ◽  
Fast Inactivation ◽  
Giant Fiber ◽  
Experimental Conditions ◽  
Giant Axons ◽  
External K

Inactivation of delayed rectifier K conductance (gK) was studied in squid giant axons and in the somata of giant fiber lobe (GFL) neurons. Axon measurements were made with an axial wire voltage clamp by pulsing to VK (∼−10 mV in 50–70 mM external K) for a variable time and then assaying available gK with a strong, brief test pulse. GFL cells were studied with whole-cell patch clamp using the same prepulse procedure as well as with long depolarizations. Under our experimental conditions (12–18°C, 4 mM internal MgATP) a large fraction of gK inactivates within 250 ms at −10 mV in both cell bodies and axons, although inactivation tends to be more complete in cell bodies. Inactivation in both preparations shows two kinetic components. The faster component is more temperature-sensitive and becomes very prominent above 12°C. Contribution of the fast component to inactivation shows a similar voltage dependence to that of gK, suggesting a strong coupling of this inactivation path to the open state. Omission of internal MgATP or application of internal protease reduces the amount of fast inactivation. High external K decreases the amount of rapidly inactivating IK but does not greatly alter inactivation kinetics. Neither external nor internal tetraethylammonium has a marked effect on inactivation kinetics. Squid delayed rectifier K channels in GFL cell bodies and giant axons thus share complex fast inactivation properties that do not closely resemble those associated with either C-type or N-type inactivation of cloned Kv1 channels studied in heterologous expression systems.

Chara buckellii, a euryhaline charophyte from an unusual saline environment. II. Membrane potential and membrane conductance at steady state

1987 ◽  
Vol 65 (2) ◽  
pp. 222-229 ◽  
Author(s):  
Rosanne Hoffmann ◽  
Mary A. Bisson
Keyword(s):  
Steady State ◽  
Membrane Potential ◽  
Membrane Conductance ◽  
Proton Pumping ◽  
Membrane Properties ◽  
Saline Environment ◽  
High Ph ◽  
Threefold Increase ◽  
Cells Cultured ◽  
External K

Electrophysiological experiments were performed on internodal cells of Chara buckellii cultured in saline and freshwater media to see whether the membrane potential (Evo) and membrane conductance (Gm) are dominated by passive K+ conductance (K state), passive H+ conductance (H state), or active proton pumping (P state). Unlike other euryhaline charophytes, C. buckellii cells cultured under saline conditions were not dominated by any one state, showing little dependence on external K+ concentration and pH (pH°). Chara buckellii cells cultured in freshwater share some membrane properties with other freshwater charophytes. Freshwater cells appeared to be in the P state between pH° 5 and 7 as expected but never attained the H state usually observed at high pH° (> 10). Freshwater cells also showed a temporary, threefold increase in Gm at pH° 5, which could not be explained by an increase in passive Cl− or K+ conductance. Evidence consistent with an electrogenic Cl−/2H+ symport in freshwater-grown C. buckellii at pH° 5 and 7 is also presented.

scholarly journals Sodium and potassium fluxes and membrane potential of human neutrophils: evidence for an electrogenic sodium pump.

1982 ◽  
Vol 79 (3) ◽  
pp. 453-479 ◽  
Author(s):  
L Simchowitz ◽  
I Spilberg ◽  
P De Weer
Keyword(s):  
Membrane Potential ◽  
Sodium Pump ◽  
Membrane Conductance ◽  
Human Neutrophils ◽  
Constant Field ◽  
Electrogenic Sodium Pump ◽  
Na Efflux ◽  
The Individual ◽  
Sodium And Potassium ◽  
External K

Sodium and potassium ion contents and fluxes of isolated resting human peripheral polymorphonuclear leukocytes were measured. In cells kept at 37 degrees C, [Na]i was 25 mM and [K]i was 120 mM; both ions were completely exchangeable with extracellular isotopes. One-way Na and K fluxes, measured with 22Na and 42K, were all approximately 0.9 meq/liter cell water . min. Ouabain had no effect on Na influx or K efflux, but inhibited 95 +/- 7% of Na efflux and 63% of K influx. Cells kept at 0 degree C gained sodium in exchange for potassium ([Na]i nearly tripled in 3 h); upon rewarming, ouabain-sensitive K influx into such cells was strongly enhanced. External K stimulated Na efflux (Km approximately 1.5 mM in 140-mM Na medium). The PNa/PK permeability ratio, estimated from ouabain insensitive fluxes, was 0.10. Valinomycin (1 microM) approximately doubled PK. Membrane potential (Vm) was estimated using the potentiometric indicator diS-C3(5); calibration was based on the assumption of constant-field behavior. External K, but not Cl, affected Vm. Ouabain caused a depolarization whose magnitude dependent on [Na]i. Sodium-depleted cells became hyperpolarized when exposed to the neutral exchange carrier monensin; this hyperpolarization was abolished by ouabain. We conclude that the sodium pump of human peripheral neutrophils is electrogenic, and that the size of the pump-induced hyperpolarization is consistent with the membrane conductance (3.7-4.0 microseconds/cm2) computed from the individual K and Na conductances.

Characteristics of active Na transport in intact cardiac cells

1979 ◽  
Vol 236 (2) ◽  
pp. H189-H199 ◽  
Author(s):  
H. G. Glitsch
Keyword(s):  
Heart Muscle ◽  
Muscle Cells ◽  
Cardiac Cells ◽  
Na Transport ◽  
Concentration Gradients ◽  
Experimental Conditions ◽  
Na Pump ◽  
Na Efflux ◽  
Heart Muscle Cells ◽  
K Concentration

An active Na transport maintains the Na and K concentration gradients across the cell membrane of many cells and restores them following excitation. Heart muscle cells display frequent electrical discharges and thus the cardiac Na pump is of fundamental functional significance. Some methods for studying active Na transport are described. The active Na efflux from heart muscle cells is activated by an increase in the intracellular Na and the extracellular K concentration. The linkage between active Na efflux and active K influx varies widely according to the experimental conditions. The cardiac Na pump is electrogenic and can contribute directly to the membrane potential of the cells. The effects of active Na transport on contraction and intercellular coupling in myocardium are discussed.

Changes in absorption, fluorescence, dichroism, and birefringence in stained giant axons: Optical measurement of membrane potential

1977 ◽  
Vol 33 (1) ◽  
pp. 141-183 ◽  
Author(s):  
W. N. Ross ◽  
B. M. Salzberg ◽  
L. B. Cohen ◽  
A. Grinvald ◽  
H. V. Davila ◽  
...  
Keyword(s):  
Membrane Potential ◽  
Optical Measurement ◽  
Giant Axons

scholarly journals Ion Transport in Hydrodictyon africanum

1967 ◽  
Vol 50 (6) ◽  
pp. 1607-1625 ◽  
Author(s):  
J. A. Raven
Keyword(s):  
Free Energy ◽  
Low Temperature ◽  
Electrical Potential ◽  
Bathing Solution ◽  
Electrical Potential Difference ◽  
Energy Gradient ◽  
Na Efflux ◽  
K Concentration ◽  
Net Fluxes ◽  
External K

The concentrations of K, Na, and Cl in the cytoplasm and vacuole, the tracer fluxes of these ions into and out of the cenocyte, and the electrical potential difference between bathing solution and vacuole and cytoplasm, have been measured in Hydrodictyon africanum. If the ions were acted on solely by passive electrochemical forces, a net efflux of K and Cl and a net influx of Na would be expected. Tracer fluxes indicate a net influx of K and Cl and efflux of Na in the light; these net fluxes are consequently active, with an obligate link to metabolism. The effects of darkness and low temperature indicate that most of the tracer K and Cl influx and Na efflux are linked to metabolism, while the corresponding tracer fluxes in the direction of the free energy gradient are not. Ouabain specifically inhibits the metabolically linked portions of tracer K influx and Na efflux. Alterations in the external K concentration have similar effects on metabolically mediated K influx and Na efflux. It would appear that K influx and Na efflux are linked, at least in the light.

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.

Sign in / Sign up

Export Citation Format

Share Document