Extracellular Potassium Concentration in Juvenile and Adult Rat Brain Cortex during Anoxia

Abstract

The extracellular K+ concentration, ([K]e), in the brain cortex of rats at different ages was measured by means of K+-sensitive microelectrodes. [K]e was between 3-5 mM at all ages. Following N2 inhalation there was an increase in [K]e which exhibited a sigmoid pattern in every age group. First there was a slow rate of rise which was followed by a sudden, steep increase where the [K]e rose to about 70 mM. During the subsequent 5-10 min a plateau value of about 90 mM was reached. The prominent difference between the age groups was the time until the steep rise began. The time to the steep increase in [K]e and the [K]e at the start of the steep increase was inversely related to the age of the animal. A close relation was found between the time to the start of the steep increase and the time to the last gasp during N2 breathing (r = 0.98). The different resistance to anoxia in young and adult animals may be related to differences in the ability to keep near normal K+ gradients across the cells in the brain.