Putrescine uptake and metabolism in isolated rat pancreatic acini

In addition to de novo synthesis, polyamine uptake is one of the major mechanisms in the regulation of intracellular polyamine concentrations. The aim of the present study was to investigate the uptake of putrescine (PUT) in isolated rat pancreatic acini and its further metabolic transformation. PUT accumulation was nearly linear over 60 min, showed saturation kinetics with an apparent Km of 3 x 10(-5) M and a Vmax of 346 pmol [14C]-PUT/min/mg DNA and decreased with decreasing temperature. Potassium cyanide (KCN) and dinitrophenol (DNP) inhibited PUT uptake. In the absence of a transmembrane Na+ gradient, PUT uptake decreased by 50%. After 60 min of incubation, 31% of the accumulated [14C]-PUT was metabolized. PUT uptake was stimulated by several amino acids, except for lysine, by decreasing the apparent Km for PUT uptake. PUT accumulation was reduced by spermidine (0.1 mM) by about 90%. Acetylated polyamines had only a minor effect. The release of radioactive material from prelabelled acini was only 10-20% after 90 min.