TIME-COURSE OF CHANGES IN EXTRACELLULAR LACTATE EVOKED BY TRANSIENT K-INDUCED DEPOLARIZATION IN THE RAT STRIATUM()

The purpose of this study was to establish whether excessive lactate p roduction associated with local application of K+ is reflected at the extracellular level during or after the K+ challenge. Changes in extra cellular lactate were continuously monitored by microdialysis coupled to on-line fluorimetric analysis. K+-induced changes in dialysate lact ate were closely related to those of the direct current potential. Hig h K+ evoked a large and sustained negative shift of direct current pot ential onto which were superimposed a variable number of transient pea ks of further depolarisation. The initial negative shift in direct cur rent potential was associated with a decrease in dialysate lactate, bu t after each transient depolarisation, the positive shift in direct cu rrent potential indicating cell repolarisation was associated with a m arked increase in extracellular lactate. When repetitive transient dep olarisations occurred during a stimulus, only a small increase after e ach depolarisation was observed. However, recordings consistently reve aled a marked and rapid increase in extracellular lactate after the K stimulus. These data indicate that extracellular lactate mostly incre ased during periods of repolarisation. This suggests strongly that lac tic acid transport out of brain cells may be impaired when their trans membrane ionic gradients are disrupted.