Regulatory interrelations between GABA and polyamines. II. Effect of GABA on ornithine decarboxylase and putrescine levels in cell culture.

GABA added to rat hepatoma (HTC) cells in spinner culture at the time of induction of cell proliferation increased levels of ornithine decarboxylase (ODC) up to two- to threefold above that of control cells. The increases in ODC were also reflected by concomitant increases of intracellular putrescine levels, while spermidine and spermine were unchanged. GABA seems to have a direct stabilizing effect on ODC, since the turnover of the enzyme was slowed almost twofold when measured in cells treated with 10(-2) M GABA. The stabilizing effect is most pronounced for GABA, although some amino acids such as asparagine, glutamine, and lysine as well as some GABA analogues and homologues also tend to increase ODC but to a significantly lesser extent than GABA itself. GABA metabolites had no effect on ODC. S-Adenosylmethionine decarboxylase and tyrosine aminotransferase were not affected by the presence of GABA. The GABA effect on ODC may be important in certain types of cells for the regulation of polyamine biosynthesis.