Transport and metabolism of agmatine in rat hepatocyte cultures

Rat hepatocytes in culture take up [14C]-agmatine by both a high-affinity transport system [KM = 0.03 mM; Vmax = 30 pmol x min x (mg protein)-1] and a low-affinity system. The high-affinity system also transports putrescine, but not cationic amino acids such as arginine, and the polyamines spermidine and spermine. The rate of agmatine uptake is increased in cells deprived of polyamines with difluoromethylornithine. Of the agmatine taken up, 10% is transformed into polyamines and 50% is transformed into 4-guanidinobutyrate, as demonstrated by HPLC and MS. Inhibition by aminoguanidine and pargyline shows that this is due to diamine oxidase and an aldehyde dehydrogenase. 14C-4-aminobutyrate is also accumulated in the presence of an inhibitor of 4-aminobutyrate transaminase.