Phorbol Ester Interferes with [3H]Norepinephrine Accumulation into Monolayers of PC 12 Cells by Stimulating the Release of Endogenous Norepinephrine.

In this study we have observed an inhibition of the [3H]norepinephrine ([3H]NE) accumulation into rat phaeochromocytoma PC 12 cells by phorbol 12-myristate 13-acetate (PMA), whereas a biologically inactive phorbol ester was without effect. The inhibition was no longer observed when the PC 12 cells were preincubated with 10 microM reserpine, which inhibits the uptake of norepinephrine into the storage vesicles. This suggested a role of the intact vesicles in the inhibitory phenomenon.