Somatostatin Biosynthesis by Cerebral Cortical Cells in Monolayer Culture*

Abstract

The ability of isolated rat cerebral cortical cells to synthesize and secrete immunoreactive somatostatin (IRS) was examined. Dispersed telencephalic cells (107) from rat embryos contain approximately 24 pg IRS. The IRS content of 107 cultured cells increased steadily to a level of 2800 pg by 20 days in vitro. The IRS content in the medium followed a parallel production curve and was, in general, 10% of the cellular content. The nature of this IRS was characterized by gel filtration. Bio-Gel P-10 chromatography resolved 4 discrete IRS peaks: The 1st peak had an apparent MW of 11,500; the 2nd peak, which comigrated with synthetic Somatostatin-28, had a MW of 7000; the 3rd peak had a MW of 1800; and the 4th peak, which comigrated with Somatostatin-14, had a MW less than 1800. Incubation with [3H]phenylalanine (Phe) revealed that 3H was incorporated into each peak. Isolation of 3H-labeled peak 4 was carried out by double affinity column purification. Sequential automated Edman degradation of this material revealed [3H] Phe in the positions that Phe occupies in Somatostatin-14. These studies document the ability of isolated rat cerebral cortical tissue to synthesize several forms of IRS, establishing them as endogenous cortical peptides.