The effects of ATP on the interactions between monovalent cations and the sodium pump in dialysed squid axons

Beaugé, Luis; Polo, Reinaldo Di

doi:10.1113/jphysiol.1981.sp013719

Cited by 29 publications

(10 citation statements)

References 44 publications

(54 reference statements)

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“…It is therefore not surprising that studies in intact cells have failed to show changes of K affinity produced by changing ATP. It is noteworthy that Pi was zero in the dialysed squid axons used to demonstrate the effects of ATP on the K affinity (Beauge & DiPolo, 1979, 1981. We have found (D. A. Eisner & D. E. Richards, in preparation) that when ghosts are prepared to contain inorganic phosphate, changing ATP produces non-parallel Lineweaver-Burk lines.…”

Section: Discussionmentioning

confidence: 96%

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The interaction of potassium ions and ATP on the sodium pump of resealed red cell ghosts.

Eisner¹,

Richards²

1981

The Journal of Physiology

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SUMMARY1. Ouabain-sensitive K or Rb influx was measured into ghosts resealed to contain ATP concentrations of 1 ,uM-3 mm and no K.2. Increasing ATP from 1 to 100#sM, at saturating external K, increased K influx about twentyfold while having no effect on the ratio of ouabain-sensitive K influx to ouabain-sensitive ATPase activity.3. Increasing external K decreased the apparent affinity for ATP. Similarly increasing ATP decreased the apparent affinity for external K.4. The K influx can be empirically described as: influx = VmaxK2/(K + Kapp)2. Increasing ATP increased Vmax and (Kapp)2 by the same amount.5. These results are consistent with a consecutive model for the Na pump in which an ATP-dependent reaction follows a K-activated dephosphorylation.

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Section: Discussionmentioning

confidence: 96%

“…Recent work in the squid axon, however, has shown that lowering ATP increases the affinity for external K as an activator of the Na efflux (Beauge6 & DiPolo, 1979, 1981.…”

Section: Ko+ep -E2k-e +Kimentioning

confidence: 99%

The interaction of potassium ions and ATP on the sodium pump of resealed red cell ghosts.

Eisner¹,

Richards²

1981

The Journal of Physiology

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“…A ping-pong kinetic mechanism for the cation transport of this kind, now firmly established for the Na-K pump (see, for example Sachs, 1979Sachs, , 1980Eisner & Richards, 1981Beauge & Di Polo, 1981) will only give a form V = Vmax([Na]/[Na] + [K])3 if it is the step following Na binding that is rate limiting.…”

Section: Stoicheiometry Vermu8 Sigmoidicitymentioning

confidence: 99%

Cation activation of the pig kidney sodium pump: transmembrane allosteric effects of sodium.

Karlish¹,

Stein²

1985

The Journal of Physiology

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SUMMARY1. We have studied activation by Na or Rb ions of different transport modes of the Na-K pump, using phospholipid vesicles reconstituted with pig kidney Na-K-ATPase. The shape of the activation curves, sigmoid or quasi-hyperbolic, depends on the nature of the cation at the opposite surface and not on the specific mode of transport.2. ATP-dependent Na uptake into K-containing vesicles (Na-K exchange) is activated by cytoplasmic Na along a highly sigmoid curve Jn the absence of extracellular Na (Hill number, nH = 1P9). Activation displays progressively lesssigmoid curves as extracellular Na is raised to 150 mm (nH = 1-2). The maximal rate of the Na-K exchange is not affected.3. Na is not transported from the extracellular face by the pump in the presence of excess extracellular K, and the transmembrane effects of the extracellular Na are therefore 'allosteric' in nature.4. ATP-dependent Na-Na exchange (Lee & Blostein, 1980) and classical ATPplus-ADP-dependent Na-Na exchange are activated by cytoplasmic Na along hyperbolic curves. ATP-dependent Na uptake into Tris-containing vesicles is activated by cytoplasmic Na along a somewhat sigmoidal curve. affect the maximal rate of exchange. 6. Slow passive Rb fluxes through the pump observed in the absence of other pump ligands (see Karlish & Stein, 1982a) are activated by cytoplasmic Rb along a strictly hyperbolic curve with extracellular Rb, nH = 1I0 (Rb-Rb exchange), along a strongly sigmoid curve with extracellular Na, nH = 15 (Rb-Na exchange), and along lesssigmoid curves with extracellular Tris, nH = 1-24 (net Rb flux) or extracellular Li, nH = 1-2 (Rb-Li exchange). Activation of the passive Rb fluxes by extracellular Rb is hyperbolic in the presence of cytoplasmic Rb, Li or Tris but is sigmoid in the presence of cytoplasmic Na (nH = 1-36). S. J. D. KARLISH AND W. D. STEIN7. Inhibition by cytoplasmic Na of passive Rb fluxes from the cytoplasmic to the extracellular face of the pump depends on the nature of the cation at the extracellular surface. In the presence of extracellular Na, cytoplasmic Na is a good inhibitor (half-maximal concentration, Ko.5 -0 5 mM). In the presence of extracellular Rb, K, Cs or NH4, cytoplasmic Na is a poor inhibitor (Ko.5 -10-20 mM), and an intermediate situation pertains with extracellular Tris or Li. Inhibition by extracellular Na of the passive Rb flux from the extracellular to cytoplasmic surface of the pump also depends on the nature of the cation at the cytoplasmic surface. Only with cytoplasmic Na is significant inhibition by extracellular Na observed (Ko.5 -5 mm).8. A kinetic analysis ofping-pong schemes for active Na-K exchange and for Rb-Rb exchange, in which more than one cation must be bound per cycle before transport occurs, shows that neither the conventionally used kinetic equation V = Vmax (S/(S+K))n nor the Hill equation V= VmaxSn/(Sn+K) should fit the data rigorously over wide ranges of substrate concentrations. The experimental data for cytoplasmic Na activation of Na-K exchange conform with this expectation.9. T...

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“…The external solutions had 200 nM TTX, a concentration high enough to block sodium channels [31]. In axons with 40 mM Na þ i , 440 mM Na þ o , no internal Ca 2+ and a membrane potential of −50 mV, ATP depletion reduces the efflux of Na + to around 0.5-1.0 pmol cm −2 s −1 , which is the value to be expected for electrodiffusion [32,33].…”

Section: Intracellular Dialysis Of Squid Giant Axonsmentioning

confidence: 98%

In the squid axon Na+/Ca2+ exchanger the state of the Cai-regulatory site influences the affinities of the intra- and extracellular transport sites for Na+ and Ca2+

DiPolo

Beaugé

2008

Pflugers Arch - Eur J Physiol

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In squid axons, intracellular Mg2+ reduces the activity of the Na+/Ca2+ exchanger by competing with Ca2+ i for its regulatory site. The state of the Ca i-regulatory site (active-inactive) also alters the apparent affinity of intra- and extracellular transport sites. Conditions that hinder the binding of Ca2+ i (low pH i, low [Ca2+]i, high [Mg2+]i) diminish the apparent affinity of intracellular transport sites, in particular for Na i due to its synergism with H+ inhibition, but less noticeably for Ca2+ i because of its antagonism towards (Ha i + Na+ i) and Mg2+ i inhibitions. These are kinetic effects unrelated to the true affinity of the sites. With the Ca i-regulatory site saturated, the intracellular transporting sites are insensitive to [H+]i and to ATP. Likewise, the state of the Ca i-regulatory site (activated or inactivated) influences the affinity of the extracellular Ca o and Na o-transport sites (trans effects). In this case, the effects are opposite to those predicted by any of the transport schemes proposed for the Na+/Ca2+exchanger; i.e. its mechanism remains unexplained. In addition to their intrinsic importance for a full understanding of the properties of the Na+/Ca2+ exchanger, these findings show a new way by which the state of the Ca i-regulatory site may determine net movements of Ca2+ through this system.

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The effects of ATP on the interactions between monovalent cations and the sodium pump in dialysed squid axons

Cited by 29 publications

References 44 publications

The interaction of potassium ions and ATP on the sodium pump of resealed red cell ghosts.

The interaction of potassium ions and ATP on the sodium pump of resealed red cell ghosts.

Cation activation of the pig kidney sodium pump: transmembrane allosteric effects of sodium.

In the squid axon Na+/Ca2+ exchanger the state of the Cai-regulatory site influences the affinities of the intra- and extracellular transport sites for Na+ and Ca2+

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