Epileptiform activity induced by alkalosis in rat neocortical slices: block by antagonists of N-methyl-D-aspartate.

The effects of changing extracellular pH on epileptiform activity induced by the removal of magnesium ions from the perfusing medium were studied. The proportion of bicarbonate in the artificial cerebrospinal fluid and of CO2 in the gas mixture were altered to mimic metabolic and respiratory acid-base disturbances. Changes in pH of 0.2 unit from control produced marked effects. Epileptiform activity was enhanced by alkalosis and diminished by acidosis. In normal magnesium-containing medium metabolic alkalosis (pH greater than 7.8) induced spontaneous epileptiform activity that was blocked by selective N-methyl-D-aspartate antagonists. The relevance of these findings to acid/base changes in clinical epilepsy is discussed.