Changes in amino acid influx with Na + flow in incubated slices of mouse brain

Abstract

The uptake of amino acids into slices of adult and newborn mouse brain was studied in relation to Na + flow. (1) The level of Na + and K + in incubated slices of brain depends on the ionic composition of the incubation medium. The intracellular levels of Na + in adult tissue are below, in fetal tissue above, Na + levels in the medium used. Rapid net flow into or out of the tissue can be achieved by transferring slices into media of higher or lower Na + content. (2) Under conditions of net Na + inflow, the influx of all amino acids tested increased; under conditions of net Na + outflow, the influx of all amino acids decreased, as compared to slices in ionic equilibrium. The absolute levels of Na + in the tissue under the experimental conditions had little effect on amino acid uptake. The stimulatory effect of Na + inflow and the inhibitory effect of Na + outflow could be observed at all developmental stages—in adult, newborn, and fetal tissue. (3) We conclude that ion movements influence metabolite transport; these effects are smaller in the absence of fully developed ion pumps. The direction of the net ion flow does not seem to be the main determinant: active accumulation occurred both in adult and in fetal brain, although the tissue-to-medium Na + gradients were in opposite directions; in addition, amino acid inflow occurred in the presence of Na + outflow.