Transport and steady-state accumulation of putrescine in brush-border membrane vesicles of rabbit small intestine.

Absorption of polyamines from the lumen is essential for cell proliferation in small intestine but also in other rapidly growing body tissues and tumors. Intestinal uptake of polyamines is thought to involve one or more transport systems, but the characteristics of these systems have not yet been clearly elucidated. Because high levels of putrescine have been identified in intestinal lumen, we explored kinetic, physiochemical, and structural features of uptake of this diamine across rabbit intestinal brush-border membrane vesicles (IBBMV) prepared by CaCl2 or MgCl2 precipitation procedure. Initial rates of putrescine influx were measured during 5-min incubations at 25 or 37 degrees C (optimal temperature) for concentrations of 0.45-145 microM. At both temperatures, kinetics of putrescine transport fitted a model with a single Michaelis-Menten uptake component plus a nonsaturable uptake component. At 37 degrees C, the kinetic parameters for the saturable component of putrescine uptake, Km,app and Vmax,app, were 16.8 +/- 4.7 microM and 19.9 +/- 2.8 pmol.mg protein-1.min-1, respectively. The value of the constant for the nonsaturable component of putrescine uptake (P = 0.45 +/- 0.06 x 10(-8) l.mg protein-1.s-1) suggested this component represented essentially nonspecific binding of putrescine to IBBMV. Cadaverine, spermidine, and spermine were competitive inhibitors of putrescine transport, with inhibition constants equal to 47, 117, and 219 microM, respectively. When effects of a variety of alkyldiamines and structural analogues of polyamines (1 mM) on influx of 5.6 microM putrescine were compared, cadaverine, methylglyoxal bis(guanylhydrazone) (MGBG), and cyclic derivatives of MGBG were found to exhibit the highest inhibitory potencies.(ABSTRACT TRUNCATED AT 250 WORDS)