Inhibitory effects of bulbocapnine on dopamine biosynthesis in PC12 cells.

The effects of bulbocapnine, an aporphine isoquinoline alkaloid, on dopamine biosynthesis in PC12 cells were investigated. Bulbocapnine showed 45.2% inhibition on dopamine content in PC12 cells at a concentration of 20 microM for 12 h. The IC50 value of bulbocapnine was 26.7 microM. Bulbocapnine at concentrations up to 80 microM was not cytotoxic towards PC12 cells. Tyrosine hydroxylase (TH) activity was inhibited by the treatment of bulbocapnine in PC12 cells (24.4% inhibition at 20 microM). Bulbocapnine at 20 microM also decreased the intracellular Ca2+ concentration by 12.9% inhibition relative to control in PC12 cells. However, TH mRNA level was not altered by bulbocapnine treatment. These results suggest that the inhibition of TH activity by bulbocapnine might be involved in at least one component of the reduction of dopamine biosynthesis in PC12 cells.