Potassium Fluxes in Dialyzed Squid Axons

Measurements have been made of K influx in squid giant axons under internal solute control by dialysis. With ATP(i) = 1 microM, Na(i) = 0, K influx was 6 +/- 0.6 pmole/cm(2) sec; an increase to ATP(i) = 4 mM gave an influx of 8 +/- 0.5 pmole/cm(2) sec, while ATP(i) 4, Na(i) 80 gave a K influx of 19 +/- 0.7 pmole/cm(2) sec (all measurements at approximately 16 degrees C). Strophanthidin (10 microM) in seawater quantitatively abolished the ATP-dependent increase in K influx. The concentration dependence of ATP-dependent K influx on ATP(i), Na(i), and K(o) was measured; an ATP(i) of 30 microM gave a K influx about half that at physiological concentrations (2-3 mM). About 7 mM Na(i) yielded half the K influx found at 80 mM Na(i). The ATP-dependent K influx responded linearly to K(o) from 1-20 mM and was independent of whether Na, Li, or choline was the principal cation of seawater. Substances tested as possible energy sources for the K pump were acetyl phosphate, phosphoarginine, PEP, and d-ATP. None was effective except d-ATP and this substance gave 70% of the maximal flux only when phosphoarginine or PEP was also present.