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Stereoselectivity of noradrenaline uptake into synaptic vesicles of the rat brain

Research paper by H. Matthaei, S. Pramono, A. Philippu

Indexed on: 01 Jun '88Published on: 01 Jun '88Published in: Naunyn-Schmiedeberg's Archives of Pharmacology



Abstract

To investigate the stereoselectivity of the ATP-Mg2+-dependent uptake of noradrenaline, synaptic vesicles were isolated from the rat brain by differential centrifugation and incubated with 3H-(±)-, 3H-(−)- or 14C-(+)-noradrenaline in the absence and in the presence of ATP-Mg2+. The Km values of the ATP-Mg2+-dependent uptake were found to be different for the two isomers (μmol/l): 3H(±)-noradrenaline 14.9 ± 2.2 × 10−1, 3H-(−)-noradrenaline 7.7 ± 0.5 × 10−1, 14C-(+)-noradrenaline 17.3 ± 3.7 × 10−1, whereas the VmaX of the racemate was identical with those of the two isomers (pmol/mg protein/min): 3H-(±)-noradrenaline 5.5 ± 0.4, 3H-(−)-noradrenaline 4.9 + 0.1, 14C-(+)-noradrenaline 5.1 ± 0.4. Moreover, (+)-noradrenaline inhibited competitively the ATP-Mg2+-dependent uptake of 3H-(±)-noradrenaline (Ki 19.2 + 1.0 × 10−1 μmol/l) and 3H-(−)-noradrenaline (Ki 17.7 ± 1.8 × 10−1 μmol/l), the Ki values being nearly identical with the Km of the ATP-Mg2+-dependent uptake of 14C-(+)-noradrenaline. It is concluded that the ATP-Mg2+-dependent uptake of noradrenaline into synaptic vesicles of the rat brain is stereoselective and that both isomers share the same transport system.