Uptake and Release of 14cadenine Derivatives at Beds of Mammalian Cortical Synaptosomes in a Superfusion System

Abstract (1) Synaptosomal fractions from guinea pig neocortical dispersions prepared in sucrose solutions were deposited from saline media as ‘beds’ on nylon bolting cloth. When incubated with 0.5–10 μ m ‐ 14 Cadenine or adenosine in glucose bicarbonate salines, uptake of 14 C from adenosine proceeded at about four times the rate of uptake of 14 Cadenine. This contrasted with the relative uptake of the two compounds to neocortical tissue slices or to beds made from mitochondrial fractions, where uptake was similar with the two precursors. Uptake of both precursors to synaptosome beds was much greater than uptake of inosine. (2) Synaptosome beds, 14 Cadenosine‐loaded, contained 88 per cent of the 14 C as 5′‐adenine nucleotides, the remainder being present as cyclic AMP, inosine, hypoxanthine and adenosine. When superfused, the 14 C output consisted mainly of adenosine, inosine and hypoxanthine, with some 7 per cent of 5′‐nucleotides and 4 per cent of cyclic AMP. (3) Electrical pulses and the addition of 50 m m ‐KCl each increased the efflux of 14 C from superfused 14 Cadenosine‐loaded beds. The superfusates issuing after excitation contained the same 14 C‐labelled compounds as issued before, with a small increase in the proportional yield of adenosine. The additional output of 14 C following electrical pulses was diminished by about 50 per cent by 0.5 μ m ‐tetrodotoxin while that following KCl was not affected; it was however prevented when the superfusing fluids were free of Ca 2+ .