Variation of potassium ion concentrations in the rat hippocampus specifically affects extracellular taurine levels

The effects of different K+ concentrations (3-100 mM) on both the extracellular amino acid levels and field potentials, evoked by perforant pathway stimulation, were studied 'in vivo' in the rat dentate gyrus by means of a brain dialysis device, formed by a hollow fiber plus a stainless-steel electrode. Perfusion with low K+ concentrations (3-12 mM; Krebs-Ringer bicarbonate) specifically enhanced the dialysate levels of taurine and concomitantly increased the population spike amplitude. High K+ concentrations in perfusate (greater than 25 mM) did not further increase the levels of taurine but enhanced both glutamate and gamma-aminobutyric acid levels, whereas the population spike diminished drastically. The absence of calcium ions in the perfusion liquid increased both basal and K+-enhanced taurine levels. The specific enhancement of extracellular taurine by physiological K+ concentrations may represent an autoregulative mechanism of nervous tissue excitability.