The ouabain‐sensitive fluxes of sodium and potassium in squid giant axons

Abstract

SUMMARY1. Fifty to ninety per cent of the Na efflux from axons of Loligo forbesi is inhibited by ouabain. The properties of the ouabain-sensitive component of the Na efflux are different from those of the ouabain-insensitive component.2. In unpoisoned axons with an average Na content of 75 m-mole/kg axoplasm the bulk of the ouabain-sensitive Na efflux is dependent on external K.3. In the presence of 460 mm Na in the external medium, raising the external K concentration from 0 to 100 mm increases the ouabain-sensitive Na efflux along a sigmoid curve which shows signs of saturating at high K concentrations.4. The curve relating ouabain-sensitive K influx to external K concentration is similar in shape to that for the ouabain-sensitive Na efflux. At all K concentrations examined the ouabain-sensitive K influx was less than the ouabain-sensitive Na efflux.5. Potassium-free sea water acts rapidly in reducing the Na efflux. There is no appreciable difference between the rates of action of K-free sea water on the Na pump and Na-free sea water on the action potential.6. Caesium and Rb can replace external K in activating the ouabainsensitive Na efflux. Both the affinity and maximum rate of the Na efflux mechanism are lower when Cs replaces K as the activating cation. P. F. BAKER AND OTHERS 7. Isosmotic replacement of external Na by either choline or dextrose, but not Li, increases the affinity of the ouabain-sensitive Na efflux mechanism for external K without appreciably affecting the maximum rate of pumping. External Li behaves like external Na and exerts an inhibitory action on the Na efflux.8. There is a large ouabain-sensitive Na efflux into K-free choline or dextrose sea waters. Addition of either Na or Li to the external medium reduces this efflux along a section of a rectangular hyperbola. The properties of this efflux suggest that there is a residual K concentration of up to 2 mm immediately external to the pumping sites in the axolemma.9. Over the range of internal Na concentrations studied (16-140 mmole/kg axoplasm) the ouabain-sensitive Na efflux increased linearly with Na concentration.10. Tetrodotoxin (10-6 g/ml.) reduces the Na influx by about half, but does not affect the ouabain-sensitive Na efflux.11. Isobutanol (1 % v/v) reversibly decreases both the ouabain-sensitive and ouabain-insensitive components of the Na efflux.12. Application of 2 mm cyanide to axons immersed in K-free sea water produces a transient rise in the Na efflux. This rise is not seen if ouabain is included in the sea water. The rise in efflux occurs at a time when the axons are partially poisoned and contain adenosine triphosphate (ATP) but no arginine phosphate (ArgP). A similar, but maintained rise can be obtained after application of dinitrophenol (DNP) at pH 8-0. The increased Na efflux in these partially poisoned axons is also inhibited by ouabain.13. Under conditions of partial-poisoning by alkaline DNP, there is a ouabain-sensitive Na influx from K-free sea water. The ouabain-sensitive Na influx is of similar size to the ouab...

Potential dependency of the electrogenic Na+-pump current in bullfrog atrial muscles.

“…The Vmax for Rb+ was almost the same as the Vmax for K+ but the Vmax for Cs~ or Li+ was somewhat lower. A similar finding has been reported for the squid axon (BAKER et al, 1969), frog skeletal muscle (BEAUGE,1975), and sheep Purkinje fiber (EISNER and LEDERER, 1980). Vol.…”

Effect of ouabain and metabolic inhibitors on the Na and K movements of nucleotide contents of L cells

“…At the maximum [Na]i reached (60 m-mole/l. cell water) in these experiments, there was no evidence of a saturation of the Na efflux, a result similar to that in squid axon (Baker et al 1969 …”

“…The immediate effect of ouabain application is to decrease the Na efflux by 0-68 p-mole/cm2 sec and the K influx by 0-46 p-mole/cm2 sec with no change in Na influx or the K efflux. If each ouabain molecule binds to a pump site and inactivates it then these pumps transfer three molecules of Na and two molecules of K, a figure similar to that found in R.B.C.S and nerve (Garraham & Glymn, 1967;Baker et al 1969).…”

“…It is well known (see Baker et al 1969) that no one method may be used to define the active transport of Na and K across a cell's membrane. The present work also shows this.…”

Effects of Lithium Ions on Electrical Activity in Sympathetic Ganglia of the Bullfrog

“…is generated by activation of the electrogenic sodium pump (Koketsu & Nishi, 1967;Nishi & Koketsu, 1968b). The sodium efflux may be accelerated when the extracellular sodium ions are totally replaced by lithium ions (Beauge & Sjodin, 1968;Baker, Blaustein, Hodgkin & Steinhardt, 1969). In any case, the intracellular sodium concentration would be reduced in a preparation soaked successively in sodium-free sucrose and sodium-free lithium solution.…”