Effects of barium on stimulus-induced rises of [K+]o in human epileptic non-sclerotic and sclerotic hippocampal area CA1.

In the hippocampus of patients with therapy-refractory temporal lobe epilepsy, glial cells of area CA1 might be less able to take up potassium ions via barium-sensitive inwardly rectifying and voltage-independent potassium channels. Using ion-selective microelectrodes we investigated the effects of barium on rises in [K+]o induced by repetitive alvear stimulation in slices from surgically removed hippocampi with and without Ammon's horn sclerosis (AHS and non-AHS). In non-AHS tissue, barium augmented rises in [K+]o by 147% and prolonged the half time of recovery by 90%. The barium effect was reversible, concentration dependent, and persisted in the presence of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA), N-methyl-D-aspartate (NMDA) and gamma-aminobutyric acid [GABA(A)] receptor antagonists. In AHS tissue, barium caused a decrease in the baseline level of [K+]o. In contrast to non-AHS slices, in AHS slices with intact synaptic transmission, barium had no effect on the stimulus-induced rises of [K+]o, and the half time of recovery from the rise was less prolonged (by 57%). Under conditions of blocked synaptic transmission, barium augmented stimulus-induced rises in [K+]o, but only by 40%. In both tissues, barium significantly reduced negative slow-field potentials following repetitive stimulation but did not alter the mean population spike amplitude. The findings suggest a significant contribution of glial barium-sensitive K+-channels to K+-buffering in non-AHS tissue and an impairment of glial barium-sensitive K+-uptake in AHS tissue.