Catecholamine Release and Uptake in Isolated Adrenergic Nerve Granules

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Abstract
Isolated storage granules from bovine splenic nerves, incubated in neutral isotonic K‐phosphate give off noradrenaline at rates rapidly increasing with temperature. Noradrenaline in concentrations of 10—20μg/ml in the incubation fluid inhibits or prevents the release. The noradrenaline thus retained is released at the normal rate after removal of the amine in the incubation fluid. After depletion, the granules are able to take up noradrenaline and adrenaline to about the original content when exposed to catecholamines in concentrations of 10—20μg/ml, suggesting a limited storage capacity of the granules. It is suggested that the noradrenaline in the adrenergic nerve terminals is partly present in a free pool available for immediate release during nerve stimulation and that a lowering of the concentration in this pool causes the granules to give off the stored transmitter until an equilibrium is reached. The following resynthesis is assumed to continue until the free pool has reached a concentration preventing further release from the granules. This concentration is about the same as that normally found in bovine splenic nerves.