Ion transport and energy metabolism in brain

The kinetics of extracellular K+ activity was compared to the availability of energy in the cortex of rats and gerbils exposed to anoxia, hypoxia, spreading depression, and ischemia. A combined K+/DC surface electrode was used alone or together with a fiber optic light guide in various experiments. All experiments were done on slightly anesthetized animals that were practically awake. The results can be summarized in the following conclusions: (1) Under conditions such as hypoxia or ischemia, K+0 showed a two-phase efflux kinetics, and a transition or critical point was reached where the response proceeds at a higher rate. This critical point was in the range of 10-16 mEq/1 potassium. (2) Availability of oxygen is necessary but not sufficient for a full rate of recovery from a long-term oxygen-deprivation insult. (3) There is an energy debt or energy-transduction bottleneck formed during a prolonged O2 insufficiency. This debt is reversed slowly during the recovery phase even when full restitution of O2 supply and blood flow has occurred.