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J Physiol. Jul 1972; 224(2): 463–475.
PMCID: PMC1331500

Inhibition of the sodium pump in squid axons by cardiac glycosides: dependence on extracellular ions and metabolism


1. The rate of inhibition of the Na pump by ouabain was examined both by direct measurement of the rate of decline of the Na efflux and by the binding of [3H]ouabain.

2. The onset of inhibition of the Na efflux was concentration-dependent; but did not follow simple first order kinetics. The time course of inhibition was roughly exponential although in about 30% of the axons inhibition was preceded by a transient stimulation of the Na efflux.

3. Inhibition of the Na efflux by both ouabain and strophanthidin was apparently irreversible.

4. The onset of inhibition was slowed markedly at low temperatures.

5. Replacement of external Na by choline, dextrose or potassium slowed the rate of inhibition. Li behaved like Na and inhibition was faster in K-ASW than in choline-ASW.

6. The rate of inhibition of Na-Na exchange was similar to that of Na-K exchange, but ouabain failed to bind securely to fully poisoned axons.

7. Two components of [3H]ouabain-binding could be distinguished. A linear component which probably reflects uptake into the cells and a saturable component which seems to reflect binding to Na-pumping sites.

8. The saturable component of binding followed a similar time course to the inhibition of the Na efflux and the rate of binding was reduced in choline-ASW and in fully poisoned axons.

9. Measurements of [3H]ouabain-binding indicate that the number of Na pumping sites in the axon membrane is probably between 103 and 1042.

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Selected References

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  • Baker PF, Blaustein MP, Keynes RD, Manil J, Shaw TI, Steinhardt RA. The ouabain-sensitive fluxes of sodium and potassium in squid giant axons. J Physiol. 1969 Feb;200(2):459–496. [PMC free article] [PubMed]
  • Baker PF, Hodgkin AL, Ridgway EB. Depolarization and calcium entry in squid giant axons. J Physiol. 1971 Nov;218(3):709–755. [PMC free article] [PubMed]
  • Baker PF, Manil J. The rates of action of K+ and ouabain on the sodium pump in squid axons. Biochim Biophys Acta. 1968 Mar 1;150(2):328–330. [PubMed]
  • Baker PF, Shaw TI. A comparison of the phosphorus metabolism of intact squid nerve with that of the isolated axoplasm and sheath. J Physiol. 1965 Sep;180(2):424–438. [PMC free article] [PubMed]
  • Baker PF, Willis JS. On the number of sodium pumping sites in cell membranes. Biochim Biophys Acta. 1969;183(3):646–649. [PubMed]
  • Baker PF, Willis JS. Potassium ions and the binding of cardiac glycosides to mammalian cells. Nature. 1970 May 9;226(5245):521–523. [PubMed]
  • Baker PF, Willis JS. Binding of the cardiac glycoside ouabain to intact cells. J Physiol. 1972 Jul;224(2):441–462. [PMC free article] [PubMed]
  • Brinley FJ, Jr, Mullins LJ. Sodium fluxes in internally dialyzed squid axons. J Gen Physiol. 1968 Aug;52(2):181–211. [PMC free article] [PubMed]
  • CALDWELL PC. The phosphorus metabolism of squid axons and its relationship to the active transport of sodium. J Physiol. 1960 Jul;152:545–560. [PMC free article] [PubMed]
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  • Keynes RD, Ritchie JM, Rojas E. The binding of tetrodotoxin to nerve membranes. J Physiol. 1971 Feb;213(1):235–254. [PMC free article] [PubMed]
  • Landowne D, Ritchie JM. The binding of tritiated ouabain to mammalian non-myelinated nerve fibres. J Physiol. 1970 Apr;207(2):529–537. [PMC free article] [PubMed]
  • Moore JW, Narahashi T, Shaw TI. An upper limit to the number of sodium channels in nerve membrane? J Physiol. 1967 Jan;188(1):99–105. [PMC free article] [PubMed]

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