Characterization of the inducible polyamine transporter in bovine lymphocytes

Abstract

The polyamine uptake system in bovine lymphocytes was activated by concanavalin A. The system was common to putrescine, spermidine and spermine. The K_t values for uptake activities of putrescine, spermidine and spermine were 3.7 uM, 0.38 uM and 0.23 uM in that order. The uptake activity was inhibited by carbonyl cyanide m‐chlorophenylhydrazone, gramicidin D or valinomycin in the presence of 20 mM K⁺ suggesting that polyamine uptake depends on the membrane potential. The uptake activity appeared 10 h after addition of concanavalin A, and the maximum was reached at 28 h indicating that induction of the polyamine transporter precedes the initiation of DNA synthesis. Addition of polyamine antimetabolites, such as α‐difluoromethyl‐ornithine and ethylglyoxal bis(guanylhydrazone), to the medium enhanced at least eightfold the induction of the polyamine transporter. The induction was repressed by addition of 50 uM spermidine or spermine, but not putrescine. We propose here that the induction of the membrane‐potential‐dependent polyamine transporter is regulated by the intracellular level of spermidine and spermine.