Effect of glycogen on cellular sodium and potassium uptake as studied on model systems.

Isopiestic data indicate that glycogen appreciably reduces the osmotic and activity coefficients of potassium phosphates relative to those of the corresponding sodium salts. Dimethylurea has a similar but smaller effect. This reduction of osmotic coefficients is probably due either to (1) the lesser ability of potassium ion, relative to sodium ion, to compete for water of hydration with the hydrophilic glycogen and a resultant stronger ion pairing of the potassium and phosphate ions; or to (2) the formation of a weak potassium-glycogen-phosphate complex. This behavior offers an explanation for the correlation between cellular glycogen and potassium.