EFFECTS OF SODIUM-FREE MEDIA UPON THE METABOLISM AND THE POTASSIUM AND WATER CONTENTS OF BRAIN SLICES

Abstract

Brain slices maintain a high concentration of potassium when incubated aerobically in ordinary sodium-containing low-potassium medium but the concentration falls to the level found under plain anaerobic conditions if choline, lithium, or tris-(hydroxymethyl)-aminomethane (tris) are substituted for all the sodium in the medium. With the choline medium, concentration of potassium in the tissue increases markedly if a very little sodium is present; considerably more sodium is required when the main cation present is lithium. A moderately high concentration of potassium is maintained in tissue under anaerobic conditions in sodium-containing medium when glycolysis is stimulated by pyruvate and previous aerobiosis. This high concentration is not found when sodium in the medium is replaced by choline or lithium. The potassium content of slices incubated aerobically or anaerobically with potassium replacing all sodium in the medium is higher than could be accounted for by simple equilibration of the slice fluids with the medium.The rate of oxygen uptake is not changed when choline or lithium replace all the sodium in the medium; with tris or potassium in place of sodium there is slight inhibition. Anaerobic glycolysis is increased in the choline and potassium media and slightly depressed in lithium medium. The stimulatory effect on anaerobic glycolysis of pyruvate is apparent in the sodium, choline, lithium, and potassium media but the stimulation by a preliminary period of aerobiosis does not occur in the lithium and potassium media.Under aerobic conditions swelling and "intracellular" (non-sucrose) space is not affected by replacing sodium with choline or lithium. Both are increased in the tris and, especially, in the potassium media. Under anaerobic conditions there is a striking decrease in swelling and intracellular space with the choline medium.The replacement of a small amount of salt by sucrose causes a decrease in swelling in all media, especially in the potassium medium.