AMINO ACID INCORPORATION IN VITRO INTO PROTEIN OF NEURONAL AND GLIAL CELL‐ENRICHED FRACTIONS

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Abstract
—: Slices of rabbit cerebral cortex were incubated in the presence of labelled amino acids. Following incubation, neuron‐ and gliaenriched fractions were obtained by density gradient centrifugation and the TCA‐insoluble radioactivity determined. The protein‐bound radioactivity was five to six times higher in the neuronal‐enriched fraction than in the glial‐enriched fraction after incubation with tritiated leucine. The neuronal fraction incorporated also a number of other amino acids to a higher extent than the glial fraction (neuron/glia ratio 2·5‐6). A definite dependence of incorporation on the rate of oxygenation was demonstrated. The suppression of amino acid incorporation was more marked for the neuronal fraction than for the glial fraction during incubation in relative hypoxia. An increase of potassium concentration in the incubation medium enhanced the amino acid incorporation in both fractions. Low sodium levels decreased the incorporation. Puromycin inhibited incorporation to approximately 30 per cent of control for both fractions. Addition of cycloheximide and dinitrophenol resulted in greater inhibition of incorporation in the neuronal fraction than in the neuroglial fraction. Actinomycin D did not markedly affect the incorporation in any fraction. These results are discussed in relation to in vivo and in in vitro differences for transport and incorporation of amino acids.
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