The influence of potassium on respiration and glycolysis by brain slices

Abstract

When brain slices are kept in a K free medium at 0[degree] they rapidly lose most of their K without serious change in their O2 uptake as subsequently measured at 38[degree]. The rate of O2 uptake by K depleted slices in the absence of K falls with time. It is rendered constant, and increased by 40-150%, depending on the conditions, by the presence of 3-6 m-equiv of K/l in the medium, and reaches a maximum with about 60 m-equiv./l. The respiratory activity with or without K is higher in the absence than in the presence of Ca but the effect of K is more marked in the presence of Ca. Stimulation of respiration by K in the medium does not occur in the absence of added substrate; it occurs appreciably with pyruvate, with glutamate and slightly with y-aminobutyrate as added substrates. Under aerobic conditions in the presence of glucose, cold-pretreated slices accumulate K rapidly during the first few minutes at 38[degree]. The maximum difference reached between the concentration of K in the slices and that in the medium is only about one-third of that found in vivo. This difference becomes smaller in media containing high concentrations of K. When the medium contains between 0 and 18 m-equiv. of K/l the stimulation of respiration is approximately proportional to the concentration of K in the slice. The aerobic glycolytic activity of R-de-pleted slices is appreciable in the absence of K. It is inhibited by concentrations of potassium in the medium of up to 10 m-equiv./l but rises again in the presence of higher K concentrations. The anaerobic glycolytic activity of K-depleted slices is low in the absence of K. It is stimulated by low concentrations of K and may be decreased again in the presence of higher concentrations. Respiration and gly-colysis are affected by Na in the medium and complete replacement of sodium by K gives effects which cannot be attributed to K alone.