Effects of potassium and of glutamate on swelling and on sodium and potassium content in brain-cortex slices from adult rats

Summary

Effects of potassium concentrations, varied systematically between 5 and 85 mM, on swelling and contents of potassium and sodium have been studied. The rectilinear rise of the potassium content and the chloride-dependent increase in swelling observed by other authors are confirmed. Furthermore it is demonstrated that:

• 1. the potassium-induced increase in swelling is dependent upon the presence of sodium in the medium;

• 2. the sodium content decreases significantly when the external potassium concentration is raised from 5–20 mM (a further rise to 50 mM causes a considerable increase which is not dependent on the swelling);

• 3. under conditions when no swelling occurs, the potassium content in the tissue shows a relative decline when the external potassium concentration is raised from 20–50 mM; an increase from 5–20 mM causes on the other hand, a steeper increase in potassium concentration than can be explained by diffusion;

• 4. the glutamate-induced swelling occurs in the absence of chloride in the medium, but is sodium-dependent; and

• 5. the concentrations of potassium required to cause the increase of swelling are identical to those previously observed to lead to a stimulation of oxygen uptake.

On the basis of these findings and data from the literature it is suggested that potassium concentrations exceeding 25 mM lead to an active uptake of potassium ions. This uptake probably occurs into glial cells, and counteracts the potassiuminduced passive release. Chloride follows as the counter ion.