5′‐adenine Mononucleotides Tn Synaptosomal Preparations From Guinea Pig Neocortex: Their Change on Incubation, Superfusion and Stimulation

Abstract— –(l) The contents of potassium and of ATP, ADP and AMP of homogenates of guinea pig neocortex in 0.32 M‐SUCROSE, and of synaptosomal preparations derived therefrom, were determined and effects of incubation, superfusion and stimulation of the preparation were examined. The synaptosome preparations in M‐SUCTOSe carried a smaller content of 5′‐nucleotide per unit protein than did the homogenate from which they were derived. However, the proportion of synaptosomal nucleotides present as ATP was markedly greater than in the homogenate as a whole, the adenylate energy‐charge being 83% greater in the synaptosomes than in the homogenate. Dilution of the synaptosomal preparation from the 1 M‐sucrose to isotonic sucrose, decreased the contcnt of ATP per unit protein, but did not change the sum ATP + ADP + AMP. (2) Examined as deposited beds during 5 to 20 min incubation in oxygenated glucose‐bicarbonate salines, synaptosomal K content and adenylate energy charge increased. These changes were sustained during a subsequent 40 min of incubation and also during superfusion. During such continued superfusion, electrical stimulation caused diminution of the ATP and the adenylate energy charge of the beds, as also did superfusion with fluids of increased K‐content. (3) Lactate formation by the superfused beds was relatively stable during 30 min incubation. By electrical stimulation, the rate of lactate formation was increased by up to 30%. Increase in the potassium content of superfusion fluids could however increase lactate production 2.4‐fold. The basis for these actions is discussed.