The Relation between External Potassium Concentration, Membrane Potential and Internal Ion Concentrations in Crayfish Axons

In single crayfish axons simultaneous determinations were made of membrane potential and intracellular concentrations of sodium, potassium and chloride at different external potassium concentrations. When the external potassium level was varied from 2–150 mM. internal potassium concentration remained fairly constant. At the same time internal sodium concentration decreased with more than 50 % whereas internal chloride level increased 10 times. These ion changes were accompanied by a considerable volume increase. From the data it was calculated that a net inward movement of potassium, chloride and water had occurred while a slight outward transport of sodium was noted at lower external potassium levels. When axon volume increased, observations were made indicating an increased intracellular hydrostatic pressure. In terms of the constant field equation, it appears as if the ratio P c 1: P k and possibly also P n a: P k increares when the axon is potassium depolarized.