Regulation of ornithine decarboxylase activity and polyamine transport by agmatine in rat pulmonary artery endothelial cells.

Agmatine, a product of arginine decarboxylation in mammalian cells, is believed to govern cell polyamines by inducing antizyme, which in turn suppresses ornithine decarboxylase (ODC) activity and polyamine uptake. However, since agmatine is structurally similar to the polyamines, it is possible that it exerts antizyme-independent actions on polyamine regulatory pathways. The present study determined whether agmatine inhibited ODC activity and polyamine transport in rat pulmonary artery endothelial cells (PAECs) by an antizyme-dependent mechanism. Agmatine caused time-dependent reductions in ODC activity, which occurred before increases in antizyme. Interventions that suppressed proteasome function caused large increases in ODC activity but failed to attenuate inhibitory effects of agmatine. When agmatine was present in the culture medium, 14C-polyamine uptake was competitively inhibited as evidenced by substantial elevations in K(m) values. If PAECs were incubated with agmatine for periods sufficient to increase antizyme, there were modest decreases in V(max) for putrescine and spermidine but not for spermine. These effects of agmatine on polyamine transport were insensitive to protein synthesis inhibition. Collectively, our findings show that agmatine decreases ODC activity and polyamine transport in PAECs, but a causal role for antizyme in these actions of agmatine is difficult to establish. Nevertheless, these observations are consistent with a model in which PAECs express both antizyme-1 and -2, but only the latter contributes to agmatine-mediated suppression of ODC activity.