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

Abstract

SUMMARY1. 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 ofNa pumping sites in the axon membrane is probably between 103 and 104/,u2.

The effect of ouabain on noradrenaline output from peripheral adrenergic neurones of isolated guinea‐pig vas deferens

“…Even Li, which is known not to interfere with the inhibition of Na pump by ouabain (Gorman & Marmor, 1970;Baker & Willis, 1972), and can substitute for sodium as a carrier of inward current (Hille, 1970) and thus produce action potentials (Hodgkin & Katz, 1949;Huxley & Stampfli, 1951), failed to completely substitute for Na. A certain amount of Na was always required.…”

“…6). This suggests that Li can substitute for Na in the ouabain action (Gorman & Marmor, 1970;Baker & Willis, 1972). Accordingly, the effect of Li on the noradrenaline output induced by the reintroduction of Ca in the presence of ouabain was studied.…”

Age-Dependent Brain Tissue Hydration, Ca Exchange and their Dose- Dependent Ouabain Sensitivity

“…They also have a different localization in cells: α 1 is ubiquitously distributed over the surfaces of cells, while high ouabain affinity isoforms are confined to a reticular distribution within the cellular membrane that paralleled underlying endoplasmic or sarcoplasmic reticulum, with Na + /Ca 2+ exchanger protein. The expression of these isoforms is age-dependent [20][21][22][23][24][25]. While the role of low-affinity receptors as a working molecule for Na + /K + pump is well established [25][26][27], the functional role of high-affinity receptors is still discussable [13].…”

“…The expression of these isoforms is age-dependent [20][21][22][23][24][25]. While the role of low-affinity receptors as a working molecule for Na + /K + pump is well established [25][26][27], the functional role of high-affinity receptors is still discussable [13]. Detailed investigations [28][29][30] showed that Na + / Ca 2+ exchange is regulated through the high-affinity ouabain receptors, while Na + /K + pump by means of low-affinity ones.…”

Intracellular sodium and the differentiation of amphibian embryonic neurones

“…Both were equally effective suggesting that failure of glycoside to bind to the pump (cf. Baker & Willis, 1972;Sachs, 1974) was not a contributory factor. Raising [K]o to 15 mm, to ensure that the sodium pump was fully activated despite the low concentration of sodium, had no effect on the consequences of sodium removal for neural differentiation.…”