A novel pituitary protein (7B2)-like immunoreactivity is secreted by a rat phaeochromocytoma cell line (PC12)

High concentrations of a novel pituitary protein (7B2) have been shown to be present in the PC12 rat phaeochromocytoma cell line by radioimmunoassay. 7B2-like immunoreactivity (IR-7B2) was released from PC12 cells into the incubation medium in response to stimulation by a depolarizing concentration of K+, and this K+-evoked release was inhibited by Co2+. The major IR-7B2 in PC12 cell and medium appeared to be identical to that in porcine pituitary gland as judged by both gel permeation chromatography and by reverse-phase high performance liquid chromatography (HPLC). Gel permeation chromatography of extracts of cell and medium revealed two IR-7B2 peaks, the earlier eluting at a elution coefficient (Kav) of 0.30 and the later at a Kav of 0.54. In medium, over 90% of the IR-7B2 eluted as the earlier peak. Fractionation of extracts of cell and medium on reverse-phase HPLC showed three main IR-7B2 peaks eluting at 43, 44.5 and 46% acetonitrile/water with 0.1% trifluoroacetic acid. The findings suggest that IR-7B2 might be released by calcium-mediated exocytosis.