The extracellular potassium concentration in brain cortex following ischemia in hypo- and hyperglycemic rats.

The extracellular potassium concentration, [K+]e, was measured in the brain cortex of hypo-, normo- and hyperglycemic rats following brain ischemia. The increase in [K+]e in control rats could be characterized by 3 phases: an initial slow rate of rise where the [K+]e rose in 2 min from 3 to 9 mM followed by an abrupt, steep increase to 60 mM within 10 s and finally a slow rise to 80 mM. In the hyper- and hypoglycemic rats the same pattern appeared, but there were significant differences in the time course. The duration of the initial phase was approximately doubled in the hyperglycemic and halved in the hypoglycemic group. The [K+]e at which the steep increase was elicited was 8--10 mM in all groups. It is concluded that the duration of the initial phase is dependent upon available stores of glucose in the brain.