Dopaminergic Properties of a Somatic Cell Hybrid Line of Mouse Neuroblastoma X Sympathetic Ganglion Cells

Studies were made on the regulation of dopamine metabolism in a cell line derived by hydridization of a non‐tyrosine‐hydroxylase‐containing line of murine neuroblastoma cells with a neur‐onally‐enriched population of murine embryonic sympathetic ganglion cells. Hybrid subclones with tyrosine hydroxylase activity were selected by exposure to tyrosine‐free medium. The cells also exhibited DOPA decarboxylase activity and the subclone (named T28) with the highest specific activities of both enzymes was further characterized. The hybrid T28 line did not contain dopamine‐β‐hydroxylase activity. The specific activity of tyrosine hydroxylase as well as of DOPA decarboxylase increased significantly in T28 cultures when the cells entered the stationary phase of growth. Both of these enzymes were also induced after several days of exposure to 1 mm‐dibutyryl cyclic AMP in culture medium containing either 5% or 0.8% serum. However, maintenance in medium containing 0.8% serum alone, which inhibited cell multiplication, did not induce either enzyme. The dopamine content of T28 cells was also regulated as a function of cell density. High density (stationary phase) cultures of T28 cells contained about 300 pmol dopamine per mg protein and at least half of this endogenous amine appeared to he stored in vesicles or granules (as judged by depletion with reserpine or α‐methyl‐m‐tyramine). The T28 and other neuronal hybrid lines appear to be useful model systems for neuro‐chemical studies.