FIGURE 4

Temporal profile of extracellular K⁺ concentration ([K⁺]_e) and energy pathways linked to [K⁺]_e clearance after neuronal excitation. (A) [K⁺]_e rapidly rises and slowly falls after direct stimulation (S) of the rat brain cortex. [K⁺]_e measured with a K⁺-sensitive microelectrode reproducibly increases (each trace represents one experiment) in response to stimulation from a resting level of 3 mmol/L to a peak (denoted by 1/1), and subsequently returns to baseline with an initially faster and subsequently slower rate of decline. The time to fall to one half of the peak value (denoted by 1/2) was considered as the first half of K⁺ clearance interval (about 2 to 3 secs duration under control conditions) and the time from half the peak value to baseline (denoted as 0) as the second half of the clearance interval (about 10 to 15 secs under control conditions). (B) Inhibition of glycolysis increases the duration of the initial phase of [K⁺]_e clearance, whereas inhibition of respiration prolongs the second phase. The first and second halves of [K⁺]_e clearance times are illustrated for control conditions (gray columns), during severe hypoxia (black columns), and during exposure to iodoacetate, an inhibitor of glycolysis and glycogenolysis (white columns). All values are indicated as percentages of those under control conditions. Significant differences from control conditions are indicated by asterisks. Panel A and data in panel B are from Raffin et al, 1992.