Electric current generated by squid giant axon sodium pump: external K and internal ADP effects

1978 ◽  
Vol 235 (1) ◽  
pp. C63-C68 ◽  
Author(s):  
R. F. Abercrombie ◽  
P. de Weer
Keyword(s):  
Sodium Pump ◽  
Giant Axon ◽  
Pump Current ◽  
Membrane Resistance ◽  
Extracellular Potassium ◽  
Sodium Efflux ◽  
Steroid Sensitive ◽  
External Potassium ◽  
Loligo Pealei ◽  
External K

The operation of the sodium pump of giant axons of the squid, Loligo pealei, has been studied simultaneously in two independent ways: 1) by measuring sodium efflux with 22Na, and 2) by calculating the transmembrane current generated by the pump from measurements of membrane resistance and digitalis-sensitive membrane potential. In normal, untreated axons, the effect of increasing the external potassium concentration on both sodium efflux and pump current is similar, which suggests that Na:K pump stoichiometry remains relatively constant in the range of 0-20 mM external K. The data are compatible with a 3:2 Na:K ratio. In axons whose intracellular ADP level has been elevated by injection of L-arginine, a large, electrically silent, cardiotonic steroid-sensitive sodium efflux takes place in the absence of external potassium; this suggests that pump-mediated Na:Na exchange is 1:1 or electroneutral. Finally, elevation of external potassium levels causes the appearance, in high-ADP axons, of electrogenic pumping, with little effect on sodium efflux; hence, in contrast to what is seen in normal (low-ADP) axons, the charge translocated, per sodium ion extruded, increases sharply with increasing extracellular potassium levels.

scholarly journals The Influence of External Potassium on the Inactivation of Sodium Currents in the Giant Axon of the Squid, Loligo pealei

1969 ◽  
Vol 53 (6) ◽  
pp. 685-703 ◽  
Author(s):  
William J. Adelman ◽  
Yoram Palti
Keyword(s):  
Steady State ◽  
Membrane Potential ◽  
Membrane Conductance ◽  
Absolute Magnitude ◽  
Giant Axon ◽  
Membrane Potentials ◽  
Initial Transient ◽  
External Potassium ◽  
Loligo Pealei ◽  
External K

Isolated giant axons were voltage-clamped in seawater solutions having constant sodium concentrations of 230 mM and variable potassium concentrations of from zero to 210 mM. The inactivation of the initial transient membrane current normally carried by Na+ was studied by measuring the Hodgkin-Huxley h parameter as a function of time. It was found that h reaches a steady-state value within 30 msec in all solutions. The values of h∞, τh, αh,and ßh as functions of membrane potential were determined for various [Ko]. The steady-state values of the h parameter were found to be inversely related, while the time constant, τh, was directly related to external K+ concentration. While the absolute magnitude as well as the slopes of the h∞ vs. membrane potential curves were altered by varying external K+, only the magnitude and not the shape of the corresponding τh curves was altered. Values of the two rate constants, αh and ßh, were calculated from h∞ and τh values. αh is inversely related to [Ko] while ßh is directly related to [Ko] for hyperpolarizing membrane potentials and is independent of [Ko] for depolarizing membrane potentials. Hodgkin-Huxley equations relating αh and ßh to Em were rewritten so as to account for the observed effects of [Ko]. It is concluded that external potassium ions have an inactivating effect on the initial transient membrane conductance which cannot be explained solely on the basis of potassium membrane depolarization.

scholarly journals Axoplasmic free magnesium levels and magnesium extrusion from squid giant axons.

1976 ◽  
Vol 68 (2) ◽  
pp. 159-178 ◽  
Author(s):  
P De Weer
Keyword(s):  
Sodium Pump ◽  
Giant Axon ◽  
Magnesium Content ◽  
Magnesium Concentration ◽  
Citrate Buffer ◽  
Sodium Efflux ◽  
Loligo Pealei ◽  
Free Magnesium ◽  
Total Magnesium ◽  
Very High

The free magnesium concentration in the axoplasm of the giant axon of the squid, Loligo pealei, was estimated by exploting the known sensitivity of the sodium pump to intracellular Mg2+ levels. The Mg-citrate buffer which, when injected into the axon, resulted in no change in sodium efflux was in equilibrium with a Mg2+ level of about 3--4 mM. Optimal [Mg2+] for the sodium pump is somewhat higher. Total magnesium content of axoplasm was 6.7 mmol/kg, and that of hemolymph was 44 mM. The rate coefficient for 28Mg efflux was about 2 X 10(-3) min-u for a 500-mum axon at 22-25degreesC, with a very high temperature coefficient (Q10=4-5). This efflux is inhibited 95% by injection of apyrase and 75% by removal of external sodium, and seems unaffected by membrane potential or potassium ions. Increased intracellular ADP levels do not affect Mg efflux nor its requirement for Na+/o, but extracellularl magnesium ions do. Activation of 28Mg efflux by Na+/o follows hyperbolic kinetics, with Mg2+/o reducing the affinity of the system for Na+/o. Lanthanum and D600 reversibly inhibit Mg efflux. In the absence of both Na+ and Mg2+, but not in their presence, removal of Ca2+ from the seawater vastly increased 28Mg efflux; this efflux was also strongly inhibited by lanthanum. A small (10(-14) mol cm-2) extra Mg efflux accompanies the conduction of an action potential.

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.

Effects of pH changes on sodium pump fluxes in squid giant axon

1987 ◽  
Vol 253 (4) ◽  
pp. C547-C554 ◽  
Author(s):  
G. E. Breitwieser ◽  
A. A. Altamirano ◽  
J. M. Russell
Keyword(s):  
Sodium Pump ◽  
Maximum Velocity ◽  
Activation Parameters ◽  
Giant Axon ◽  
Inhibitory Effect ◽  
Squid Giant Axon ◽  
Extracellular Ph ◽  
Sodium Efflux ◽  
Effects Of Ph ◽  
Ph Range

The effects of independently varying intracellular and extracellular pH on sodium pump fluxes were studied in the squid giant axon. By means of intracellular dialysis, we found that changes of intracellular pH (pHi), but not of extracellular pH, affected ouabain-sensitive Na+ efflux and K+ influx over the pH range of 6.0-8.6. Both fluxes were maximum at a pHi of 7.2-7.4. Variations away from this optimal pHi in either the acidic or alkaline direction resulted in a graded inhibition of both ouabain-sensitive fluxes. The kinetic basis for the inhibitory effect of acidic pHi was examined by comparing the kinetic parameters of activation of ouabain-sensitive sodium efflux by intracellular Na+ (Na+i) and extracellular K+ (K+o) at normal pHi with those at acidic pHi. We found that the inhibitory effect of intracellular acidity results from a reversible decrease in maximum velocity (Vmax), without an effect on the activation parameters for Na+i (K1/2 Na+i) or K+o (K1/2 K+o).

Effect of Extracellular Potassium on the Transport of Sodium and Potassium in Rat Thymocytes

1981 ◽  
Vol 61 (3) ◽  
pp. 307-312 ◽  
Author(s):  
R. B. Jones ◽  
J. Patrick ◽  
P. J. Hilton
Keyword(s):  
Potassium Concentration ◽  
Extracellular Potassium ◽  
Sodium Influx ◽  
Potassium Efflux ◽  
Sodium Efflux ◽  
Extracellular Potassium Concentration ◽  
External Potassium ◽  
Potassium Influx ◽  
Sodium And Potassium

1. The effect of extracellular potassium on the transport of sodium and potassium in rat thymocytes has been studied in vitro. 2. A significant increase in the rate constant for total and ouabain-sensitive sodium efflux was demonstrated at an extracellular potassium concentration of 1 mmol/l as compared with that at either 0 or 2 mmol/l. 3. At potassium concentrations below 3 mmol/l ouabain-sensitive sodium influx was observed suggesting sodium-sodium exchange catalysed by the sodium pump. 4. Both total and ouabain-insensitive potassium efflux rose with external potassium. A small ouabain-sensitive potassium efflux was observed at all levels of external potassium studied. 5. Total and ouabain-insensitive potassium influx increased with external potassium, but did not appear to saturate. Ouabain-sensitive potassium influx reached a maximum at an external potassium concentration of 2 mmol/l then decreased with increasing external potassium.

scholarly journals Effects of Intracellular Adenosine-5'-diphosphate and Orthophosphate on the Sensitivity of Sodium Efflux from Squid Axon to External Sodium and Potassium

1970 ◽  
Vol 56 (5) ◽  
pp. 583-620 ◽  
Author(s):  
Paul De Weer
Keyword(s):  
Creatine Phosphokinase ◽  
Giant Axon ◽  
Squid Giant Axon ◽  
Squid Axon ◽  
Sodium Efflux ◽  
Excess Mg ◽  
Sodium And Potassium ◽  
External K

A study was made of sodium efflux from squid giant axon, and its sensitivity to external K and Na. When sodium efflux from untreated axons was strongly stimulated by Ko, Nao was inhibitory; when dependence on Ko was low, Nao had a stimulatory effect. Incipient CN poisoning or apyrase injection, which produces high intracellular levels of ADP1 and Pi, rendered sodium efflux less dependent on external K and more dependent on external Na. Injection of ADP, AMP, arginine, or creatine + creatine phosphokinase, all of which raise ADP levels without raising Pi levels, had the same effect as incipient CN poisoning. Pi injection had no effect on the K sensitivity of sodium efflux. Axons depleted of arginine and phosphoarginine by injection of arginase still lost their K sensitivity when the ATP:ADP ratio was lowered and regained it partially when the ratio was raised. Rough calculations show that sodium efflux is maximally Ko-dependent when the ATP:ADP ratio is about 10:1, becomes insensitive to Ko when the ratio is about 1:2, and is inhibited by Ko when the ratio is about 1:10. Deoxy-ATP mimicked ADP when injected into intact axons. Excess Mg, as well as Pi, inhibited both strophanthidin-sensitive and strophanthidin-insensitive sodium efflux. An outline is presented for a model which might explain the effects of ADP, Pi and deoxy-ATP.

scholarly journals Extracellular potassium dependence of the Na+-K+-ATPase in cardiac myocytes: isoform specificity and effect of phospholemman

2009 ◽  
Vol 297 (3) ◽  
pp. C699-C705 ◽  
Author(s):  
Fei Han ◽  
Amy L. Tucker ◽  
Jerry B. Lingrel ◽  
Sanda Despa ◽  
Donald M. Bers
Keyword(s):  
Cardiac Myocytes ◽  
Knockout Mice ◽  
Pump Current ◽  
Extracellular Potassium ◽  
Wild Type ◽  
Cytosolic Domain ◽  
Intracellular Ca ◽  
Isoform Specificity ◽  
External K

Cardiac Na+-K+-ATPase (NKA) regulates intracellular Na+, which in turn affects intracellular Ca2+ and contractility via the Na+/Ca2+ exchanger. Extracellular K+ concentration ([K+]) is a central regulator of NKA activity. Phospholemman (PLM) has recently been recognized as a critical regulator of NKA in the heart. PLM reduces the intracellular Na+ affinity of NKA, an effect relieved by PLM phosphorylation. Here we tested whether the NKA α1- vs. α2- isoforms have different external K+ sensitivity and whether PLM and PKA activation affects the NKA affinity for K+ in mouse cardiac myocytes. We measured the external [K+] dependence of the pump current generated by the ouabain-resistant NKA isoform in myocytes from wild-type (WT) mice (i.e., current due to NKA-α1) and mice in which the NKA isoforms have swapped ouabain affinities (α1 is ouabain sensitive and α2 is ouabain resistant) to assess current due to NKA-α2. We found that NKA-α1 has a higher affinity for external K+ than NKA-α2 [half-maximal pump activation ( K0.5) = 1.5 ± 0.1 vs. 2.9 ± 0.3 mM]. The apparent external K+ affinity of NKA was significantly lower in myocytes from WT vs. PLM-knockout mice ( K0.5 = 2.0 ± 0.2 vs. 1.05 ± 0.08 mM). However, PKA activation by isoproterenol (1 μM) did not alter the K0.5 of NKA for external K+ in WT myocytes. We conclude that 1) NKA-α1 has higher affinity for K+ than NKA-α2 in cardiac myocytes, 2) PLM decreases the apparent external K+ affinity of NKA, and 3) phosphorylation of PLM at the cytosolic domain does not alter apparent extracellular K+ affinity of NKA.

The Efflux of Sodium from Single Crab Muscle Fibres

1967 ◽  
Vol 47 (3) ◽  
pp. 709-721 ◽  
Author(s):  
E. E. Bittar ◽  
P. C. Caldweix ◽  
A. G. Lowe
Keyword(s):  
Normal Level ◽  
Sodium Pump ◽  
Muscle Fibres ◽  
Single Muscle ◽  
Sodium Efflux ◽  
Leg Muscles ◽  
A Value ◽  
External Potassium ◽  
Radioactive Sodium ◽  
Lactate And Pyruvate

The efflux of radioactive sodium injected into single muscle fibres from the leg muscles of Maia squinado (Herbst) has been studied. The efflux is reduced by the sodium-pump-inhibitor ouabain and by removal of the external potassium. An increase in external potassium leads to a transient increase in sodium efflux which is then followed by a decline to a value well below the normal level. Externally applied caffeine and injected calcium can, under certain conditions, cause a lowering of the sodium efflux which may be associated with contraction of the fibre. The injection of lactate and pyruvate did not affect the efflux. The results are discussed in terms of the possible effects of the structure of the fibre on the efflux.

Mutation of a conserved proline residue in the beta-subunit ectodomain prevents Na(+)-K(+)-ATPase oligomerization

1993 ◽  
Vol 265 (4) ◽  
pp. C1169-C1174 ◽  
Author(s):  
K. Geering ◽  
P. Jaunin ◽  
F. Jaisser ◽  
A. M. Merillat ◽  
J. D. Horisberger ◽  
...  
Keyword(s):  
Sodium Pump ◽  
Critical Role ◽  
Pump Current ◽  
Beta Subunit ◽  
Sequence Motif ◽  
Wild Type ◽  
Ouabain Binding ◽  
Conserved Sequence ◽  
External Potassium ◽  
And Function

A highly conserved sequence motif (4 tyrosines and 1 proline: YYPYY) of the Na(+)-K(+)-adenosinetriphosphatase (ATPase) beta 1-subunit ectodomain has been mutagenized to study its possible role in alpha/beta-assembly and sodium pump function. Single as well as double tyrosine mutants (tyrosine to phenylalanine: Y to F) of Xenopus laevis beta 1-subunits are able to associate with alpha 1-subunits and form functional Na-K pumps at the plasma membrane that are indistinguishable from wild-type alpha 1, beta 1-Na-K pumps (as assessed by measurements of ouabain binding, 86Rb flux, Na-K pump current, and activation by external potassium). In contrast, a single proline mutation (proline to glycine: P244G) reduced by > 90% the proper assembly and function of Na(+)-K(+)-ATPase, despite a normal rate of synthesis and core glycosylation. Our data indicate that proline-244 plays a critical role in the proper folding of the beta-subunit and its ability to associate efficiently with the alpha 1-subunit in the endoplasmic reticulum.

Modulation of spike frequency by regions of special axonal geometry and by synaptic inputs

1976 ◽  
Vol 39 (4) ◽  
pp. 882-899 ◽  
Author(s):  
M. E. Spira ◽  
Y. Yarom ◽  
I. Parnas
Keyword(s):  
Conduction Block ◽  
Membrane Conductance ◽  
Giant Axon ◽  
Membrane Resistance ◽  
High Frequency Stimulation ◽  
Extracellular Potassium ◽  
Synaptic Inputs ◽  
Giant Axons ◽  
Synaptic Potentials ◽  
Stimulation Of

1. Spike propagation across the nonhomogeneous section of the giant axon in ganglion T3 of the cockroach was analyzed by intracellular microelectrodes recording at the posterior and anterior ends of T3. Ascending and descending potentials were evoked by stimulation of A5-A6 and T2-T3 connectives. 2. At high frequencies, descending and ascending impulses exhibit the following: a) consecutive reduction in the spike amplitude, b) a decrease in the afterhyperpolarization; c) gradual appearance of a prepotential together with an increase in delay of spike initiation; d) failure of full spike invasion into the recording area, showing only a decremental potential. 3. The duration of a train required to block spike propagation when the whole connective is stimulated is much shorter (about 6 times) than that required when a single giant axon is stimulated. 4. The conduction block is associated with a marked decrease in effective membrane resistance, greater than that expected from depolarization and delayed rectification. 5. Synaptic potentials could be recorded in the giant axons in the caudal base of ganglion T3 after stimulation of either the ipsilateral or contralateral connectives at both ends of the ganglion. These synaptic potentials could be blocked by d-tubocurarine (d-TC) or low Ca2+-high Mg2+. 6. Activation of these synapses produces a marked increase in membrane conductance, blocking propagation of spike trains through the ganglion. 7. After these synapses are blocked by d-TC or low Ca2+-high Mg2+, high-frequency stimulation still produces a conduction block. 8. It seems that conduction of spike during repetitive stimulation is affected both by accumulation of extracellular potassium, which depolarizes the membrane and causes sodium inactivation, and by activation of synaptic inputs to shunt the membrane in this region. 8. Each of these two mechanisms by itself can produce conduction block along the giant axons in ganglion T3.

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