Linear range of Na+ pump in sciatic nerve of frog

The Na+-activated utilization of O2 by frog sciatic nerve is a linear function of the internal concentration of Na+ in preparations deprived of external Ca2+. It is assumed that this component of O2 uptake is a measure of the active extrusion of Na+ by the Na+ pump because it is suppressed by ouabain. However, no tendency toward saturation, expected in an enzymatic process with a high affinity for Na+, was evident. Similar linearity has been reported in other neuronal preparations in experiments measuring 22Na+ efflux directly. The slope of the linear relation between Na+-activated O2 uptake and the concentration of internal Na+ is independent of the external concentration of Na+, but it decreases when the external concentration of K+ is changed from 10 to 4.8 mM.