Effects of acetylcholine on potassium-induced changes of water and sodium uptakes in cerebral cortex slices from the rat.

The increases in uptakes of water and of sodium ions that occur in rat brain cortex slices when they are incubated in a physiological saline-glucose medium in presence of a high concentration of potassium ions (105 muequiv./ml) are abolished by acetylcholine in presence of eserine but not by choline. Acetylcholine is effective at 20 micron but its optimal effect occurs at about 0.7 micron. Its action is suppressed by atropine and not by d-tubocurarine. The potassium-induced change of permeability of brain cell membranes to sodium ions occurs at a site different from the tetrodotoxin-sensitive channel of sodium entry, because the suppressive effects of acetylcholine and tetrodotoxin are apparently independent of each other. The acetylcholine effect does not occur in the absence of calcium ions from the incubation medium. It is suggested that the increase of cell calcium ions, brought about by high concentrations of potassium ions in the incubation medium, induces an increase of glial permeability to sodium ions, with a resultant change in the sodium gradient, and that this increase is suppressed by acetylcholine.