S100B Secretion in Acute Brain Slices: Modulation by Extracellular Levels of Ca²⁺ and K⁺

Hippocampal slices have been widely used to investigate electrophysiological and metabolic neuronal parameters, as well as parameters of astroglial activity including protein phosphorylation and glutamate uptake. S100B is an astroglial-derived protein, which extracellularly plays a neurotrophic activity during development and excitotoxic insult. Herein, we characterized S100B secretion in acute hippocampal slices exposed to different concentrations of K⁺ and Ca²⁺ in the extracellular medium. Absence of Ca²⁺ and/or low K⁺ (0.2 mM KCl) caused an increase in S100B secretion, possibly by mobilization of internal stores of Ca²⁺. In contrast, high K⁺ (30 mM KCl) or calcium channel blockers caused a decrease in S100B secretion. This study suggests that exposure of acute hippocampal slices to low- and high-K⁺ could be used as an assay to evaluate astrocyte activity by S100B secretion: positively regulated by low K⁺ (possibly involving mobilization of internal stores of Ca²⁺) and negatively regulated by high-K⁺ (likely secondary to influx of K⁺).