EFFECTS OF TETRAHYDROPALMATINE AND SOME OTHER ISOQUINOLINE ALKALOIDS ON THE UPTAKE OF ³HDOPAMINE INTO RAT STRIATAL SYNAPTOSOMES AND VESICULAR STORE

Effects of some tetrahydroisoquinoline alkaloids on rat striatal synaptosomal uptake and vesicular storage of ³H dopamine (³HDA) have been investigated in vitro. The Km and Vmax of striatal synaptosomal ³HDA uptake were about 0.23/μmol and 1.2 nmol/g tissue (5 min) at 25℃ respectively. In our experiments, d-THP, 1-THP, 1-SPD, nomifensine, amphetamine and haloperidol all significantly decreased the accumulation of ³H DA into the striatal synaptosomes. The order of inhibitory potency (IC₅₀) of these compounds was nomifensine (0.05βmol)>d-THP(0.44 μmol), amphetamine(0.27 μmol)>1-SPD (2.2 μmol), haloperidol(3.2 μmol)>1-THP(18.5 μmol), d-THP was about 20 times more potent than 1-THP. In kinetic study, the inhibition of both d-THP and nomifensine appeared to be competitive, d-THP, similar to reserpine, also markedly inhibited the accumulation of ³H DA into vesicular store in a dose-dependent manner. Our results indicate that THP not only can inhibit potently the uptake of ³HDA into rat striatal synaptosomes but also act directly on the vesicles to reduce the ³HDA storage like reserpine.