The effect of electrical stimulation and ouabain on the uptake and efflux of l-[U-14C]valine in chopped tissue from guinea-pig cerebral cortex

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Abstract
1. Chopped tissue from guinea-pig cerebral cortex carried out an energy-dependent accumulation of l-[14C]valine. 2. The uptake was dependent on the extracellular concentration of Na+ and was markedly inhibited by ouabain (20μm). The extent of the inhibition of uptake by ouabain was also Na+-dependent. 3. The accumulation of labelled valine was not directly dependent on the ATP and creatine phosphate contents of the slices. 4. Electrical stimulation increased the rate of [14C]valine uptake at first but ultimately led to a net loss of the label so that the amount of label present in the tissue was lower than in the controls. 5. The rate of loss of label during prolonged stimulation was dependent on the extracellular concentration of Na+. 6. The efflux of labelled valine from slices preloaded at 164mm-Na+ was studied at 164, 80 and 40mm-Na+ with and without electrical stimulation or ouabain. 7. Lowering the Na+ concentration or adding ouabain increased the rate of efflux. 8. Electrical stimulation had little effect on the rate of efflux at first but ultimately led to a more complete loss of label from the tissue than occurred in the control. A kinetic analysis of the efflux curves was attempted.