Subcellular Localization of [¹⁴c]adenine Derivatives Newly‐formed in Cerebral Tissues and the Effects of Electrical Excitation

Guinea pig neocortical tissues were incubated with [ 14 C]adenine, dispersed in cold isotonic sucrose and subcellular fractions prepared by centrifugation. Some 98 per cent of the assimilated 14 C was found as acid‐soluble nucleotides in the incubated tissues. In primary fractions obtained by differential centrifugation, about 60 per cent of the [ 14 C]‐nucleotides were in supernatant fractions, in distinction to ATP of which the greatest molar quantity (61 per cent of that in the dispersion) was in the crude mitochondrial fraction. When the crude mitochondrial fraction was separated by density gradient centrifugation, most 14 C was found in synaptosomal fractions and about 85 per cent of this 14 C was adenine nucleotides. Electrical stimulation of incubating tissues immediately prior to their dispersion and centrifugation greatly diminished the proportion of 14 C subsequently found in nucleotides (collectively) in the supernatant fraction, and increased their inosine and hypoxanthine. Stimulation increased the tissue's cyclic AMP but a preferential localization for this was not established. Results are tentatively interpreted in terms of liberation of an adenine derivative on excitation, and its action or reuptake at a tissue component different from that from which it was liberated. Fractionation of tissues which had been incubated with both [ 14 C]‐adenine and [ 3 H]adenosine suggested that of the two compounds, more adenosine was taken up by synaptic regions in preference to other cellular regions of the tissue.