Anoxia in vitro does not induce neuronal swelling or death

To improve the understanding of neuronal cell swelling in cerebral ischemia, cell volume regulation, viability, intracellular electrolytes, and lactate production of Neuro-2A neuroblastoma cells were studied using an in vitro model. The volume regulatory capacity of Neuro-2A cells was assessed after incubation in hypo- and hypertonic media. Anoxia was studied alone and together with inhibition of glycolysis by iodoacetate. Reducing the tonicity of the incubation medium to 250, 200, or 150 mosm/l caused immediate swelling followed by a regulatory volume decrease within 20 min, which, however, was not complete. The final cell volume after regulation depended on the tonicity of the medium and remained above control. There was no regulatory volume increase after cell shrinking in hypertonic media. Despite the severe anisotonic incubation, viability decreased only slightly without reaching statistical significance. In contrast to in vivo conditions, anoxia for 90 min with or without iodoacetate for additional inhibition of anaerobic energy metabolism neither caused neuronal cell swelling nor a decrease of viability. Reoxygenation after the anoxic period also did not induce volume and viability changes. Intracellular K+ of Neuro-2A cells was markedly decreased, while Na+ increased in a 1:1 ratio during complete energy failure by anoxia plus iodoacetate. A similar effect, occurring however somewhat delayed, was seen when the Neuro-2A suspension was exposed to iodoacetate alone. Anoxia without inhibition of glycolysis had no effect on intracellular ion concentrations, but lactate production was nearly six times higher than normal. In vitro, with a large extracellular volume and sufficient glucose supply, the energetic demands of Neuro-2A cells to maintain stable transmembraneous ion gradients during anoxia are obviously met by anaerobic glycolysis. The current results confirm that neuronal cells are able to adequately regulate cell volume in response to hyposmotic stress. On the other hand, maintenance of a normal cell size during complete energy deprivation suggests strongly that energy failure per se does not suffice to induce neuronal swelling. Cell swelling in cerebral ischemia in vivo thus appears a secondary phenomenon due to mediator mechanisms such as tissue acidosis or elevated extracellular glutamate levels.