High concentrations of extracellular potassium enhance bacterial endotoxinlipopolysaccharide-induced neurotoxicity in glia-neuron mixed cultures

A sudden increase in extracellular potassium ions (K+) often occurs in cere bral ischemia and after brain trauma. This increase of extracellular K+ con stitutes the basis for spreading depression across the cerebral cortex, res ulting in the expansion of neuronal death after ischemic and traumatic brai n injuries. Besides spreading depression, it has become clear that cerebral inflammation also is a key factor contributing to secondary brain injury i n acute neurological disorders. Experiments to validate the relationship be tween elevated levels of extracellular K+ and inflammation have not been st udied. This study aims to elucidate the roles of high concentrations of ext racellular K+ in bacterial endotoxin lipopolysaccharide-induced production of inflammatory factors. Increased concentration of KCl in the medium (20 m M) significantly enhanced neurotoxicity by lipopolysaccharide in glia-neuro n mixed cultures. To delineate the underlying mechanisms of increased neuro toxicity, the effects of high extracellular K+ were examined by using mixed glial cultures. KCl at 20 mM significantly enhanced nitrite, an index for nitric oxide, production by about twofold, and was pronounced from 24 to 48 h, depending on the concentration of KCl. Besides nitric oxide production of tumor necrosis factor-alpha was also enhanced. The augmentative effects of high KCl on the production of inflammatory factors were probably due to the further activation of microglia, since high KCl also enhanced the produ ction of tumor necrosis factor-alpha in microglia-enriched cultures. The in creased production of nitrite by high K+ was eliminated through use of a K-blocker. Taken together, the results show that increases of extracellular K+ concent rations in spreading depression augment lipopolysaccharide-elicited neuroto xicity, because production of inflammatory factors such as nitric oxide and tumor necrosis factor-alpha are potentiated. Since spreading depression an d cerebral inflammation are important in acute neurological disorders, the present results suggest a biochemical mechanism: elevated extracellular Kconcentrations augment glial inflammatory responses, and thus the neurotoxi city. Published by Elsevier Science Ltd.