CHARACTERIZATION OF UNIVECTORIAL POLYAMINE TRANSPORT IN DUODENAL CRYPT CELL-LINE

High levels of polyamines have been identified in the lumen of the int estines. Luminal polyamines are involved in normal mucosal growth and may be the primary source of extracellular polyamines for tumors grown in animals undergoing polyamine antimetabolite therapy. The vectorial movement of polyamines across an in vitro model of the gut was studie d in epithelial cells grown in culture. IEC-6 cells were plated on eit her plastic or raised inserts. Cells grown on plastic were employed to define the kinetic constants for putrescine and spermidine uptake. Ea die-Hofstee plot analysis of putrescine uptake was characteristic of a single class of transporter with a Michaelis constant (K(m)) of 4.85 +/- 0.57 muM and a maximal velocity (V(max)) of 627 +/- 85 pmol.15 min -1.10(6) cells-1. The plot for spermidine uptake was curvilinear and r epresentative of the interaction of spermidine with two sites: K(m) 1 and 2 are 0.26 +/- 0.13 and 2.1 +/- 0.77 muM; V(max) 1 and 2 are 177 /- 50 and 429.5 +/- 70 pmol.15 min-1.10(6) cells-1, respectively. Calm odulin antagonism blocked the uptake of putrescine and the low-affinit y but not high-affinity spermidine uptake system. Seven-day postconflu ent cells grown on plastic inserts were used to study the vectorial mo vement of polyamines in a polarized epithelium. The apical membrane do main expressed two sites with similar kinetic constants to those obser ved when cells were grown on plastic. In contrast, however, the basola teral membrane did not transport polyamines. Spermidine uptake through this membrane was only a fraction of that in the apical membrane and was completely nonspecific. Polyamines were allowed to accumulate intr acellularly, and their release was subsequently determined over time. Under these conditions polyamines were released exclusively into the b asolateral compartment bathing the cell. These data demonstrate the un ivectorial movement of polyamines in an in vitro model of the gut and suggest that this functional arrangement in vivo may promote the unidi rectional movement of polyamines from gut lumen to blood.