S100B secretion in acute brain slices: modulation by extracellular levels of Ca(2+) 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 Ca(2+) in the extracellular medium. Absence of Ca(2+) and/or low K(+) (0.2 mM KCl) caused an increase in S100B secretion, possibly by mobilization of internal stores of Ca(2+). 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 Ca(2+)) and negatively regulated by high-K(+) (likely secondary to influx of K(+)).