Glucose enhances recovery of potassium ion homeostasis and synaptic excitability after anoxia in hippocampal slices

Abstract

Hippocampal slices exposed to brief anoxia combined with elevated glucose exhibit greater postanoxic recovery of synaptic transmission. Glucose may have improved recovery of synaptic transmission by enhancing the production of metabolic energy during and after anoxia. This enhancement should provide more ATP for energy-requiring ion transport processes, and lead (1) to a delayed onset of complete depolarization of CA1 pyramidal cells during anoxia (anoxic depolarization) and (2) to greater ion transport activity following anoxia. A delay in anoxic depolarization would protect neurons from damage if the duration of anoxic depolarization was shortened. Greater postanoxic ion transport would allow the re-establishment of ion gradients supportive of neuronal and synaptic excitability. The effects of glucose and anoxia on ion homeostasis and synaptic transmission were examined in rat hippocampal slices exposed to different glucose concentrations (5-20 mM). The duration of anoxic depolarization was held constant so that postanoxic damage related to this duration was controlled. We found that K+ transport and recovery of synaptic transmission after anoxia in hippocampal slices improved as glucose concentration increased. Also, anoxic depolarization was delayed as glucose concentration increased. Thus, added glucose may improve postanoxic recovery of synaptic transmission by better supporting ion transport.