TRANSPORT OF PUTRESCINE IN THE ISOLATED RABBIT INTESTINE

The transepithelial fluxes of putrescine were studied in sections of the three segments of rabbit intestine mounted in an Ussing chamber. The ileum exhibited the highest mucosal-to-serosal (J(ms)) and serosal-to-mucosal (J(sm)) unidirectional fluxes of 1-mu-mol/l [H-3]putrescine. Putrescine net flux (J(net) = J(ms) - J(sm)) was deduced to be positive through the duodenum (J(net) = 53.40 +/- 14.30 pmol h-1 cm-2), not significantly different from zero through the jejunum (J(net) = 8.90 +/- 19.20 pmol h-1 cm-2) and negative through the ileum (J(net) = -34.30 +/- 13.80 pmol h-1 cm-2). Increasing putrescine concentration up to 10 mmol/l led to an increase in J(ms), J(sm) and J(net) without affecting the transport polarity in the ileum. The tissue retention of putrescine after 100 min was higher by the serosal side than by the mucosal side of the ileum. In parallel experiments, isolated pieces of ileum accumulated putrescine to a five- to sixfold concentration gradient by a ouabain-inhibitable mechanism. In contrast with arginine and in order of decreasing potency, putrescine, cystamine (a transglutaminase inhibitor), spermidine and spermine (1 mmol/l) reduced both unidirectional fluxes of putrescine across the ileum in the Ussing chamber. The latter effectors, except spermine, and N,N-dimethylcasein (1 mg/ml) led to an important, if not complete, suppression of putrescine secretion by the ileum, while the calmodulin antagonist melittin (0.3-mu-g/ml) reversed the polarity of polyamine transport, suggesting the involvement of transglutaminase in putrescine transport. We conclude that the heterogeneous pattern of putrescine transport along the small-intestinal epithelium constitutes an important feature of the regulation of polyamine concentrations in this tissue.