Reuptake and Net Uptake of Noradrenaline in Adrenergic Nerve Granules with a Note on the Affinity for l‐ and d‐Isomers

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Abstract
The net loss of noradrenaline (NA) from bovine splenic nerve granules observed after incubation for 60 min at 20d̀ C in phosphate buffer is reduced in the presence of NA in the incubation medium. The effect is observed from 10‐7M NA and gradually increases so that at 10‐4M NA in the medium the net loss is small. By continuous removal of the NA in the medium by addition of potassium ferricyanide, the net loss reaches a maximum value which may represent the basic release rate. The effect of NA in the medium is due to reuptake of NA as indicated by the incorporation of dI‐3H‐NA in the granules during incubation. Preliminary observations suggest that the reuptake is also ATP‐dependent. During successive depletion of labelled stores at 20d̀, the specific activity of NA is unalterec indicating a uniformly labelled pool. In partially NA depleted nerve granules the net uptake of NA from the medium is enhanced by ATP‐Mg2and dependent on the NA concentration in the medium. A method for estimating the relative affinity of the l‐ and d‐isomer for nerve granules is described. The mean value found for the affinity ratio l‐NA/d‐NA was 9.4 (range 4.2–15.7). It is suggested that the continuous turnover of NA in the nerve storage granules is of major significance for the physiological transmitter homeostasis.
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