Induction of both rat and mouse lactate dehydrogenase in hybrids between inducible rat glioma and uninducible mouse neuroblastoma cells.

The specific activity of lactate dehydrogenase (LDH; EC 1.1.1.27) is induced two-fold by l-norepinephrine (NE) in C6TK- rat glioma cells, but not in NA mouse neuroblastoma cells or various other nonglial cells. Previous reports have shown that the induction is mediated by cyclic AMP (cAMP) and possibly protein phosphorylation, and that it requires RNA and protein synthesis. To study the block to LDH induction in nonglial cells, we hybridized C6TK- cells with NA cells and isolated a hybrid clone in which LDH is inducible by NE. Mouse and rat LDH from hybrid cells were separated by electrophoresis and quantitated by two independent methods, and it was found that mouse and rat LDH were induced equally when cells were exposed to NE. The results suggest that inducibility of LDH is not determined by a cis-acting control at the gene level, but rather by the presence or absence of an earlier component in the cAMP-mediated induction system, and that the induction system acts indiscriminately on all active LDH gene copies in the cell.