Interaction of N¹,N¹²-Diacetylspermine with Polyamine Transport Systems of Polarized Porcine Renal Cell Line LLC-PK

LLC-PK₁ cells grown on porous membrane filters were employed as a model system to explore the renal transport of polyamines. The polarity of LLC-PK₁ monolayers was confirmed by the exclusive appearance of a Na⁺-dependent [alpha]-methylglucoside transport system on the apical surface. The uptake of free polyamines from the basolateral side of monolayers was consistent with the existence of a single class of transport system, while the existence of two kinetically distinct polyamine transport systems with higher and lower affinities on apical membranes was suggested. The results of competition studies indicated that each of these transporters was able to interact with putrescine, spermidine and spermine. LLC-PK₁ cells incorporated monoacetylspermine from the apical surface of monolayers at about half the rate of spermine uptake. Monoacetylspermine inhibited spermidine uptake, indicating that free polyamine transport systems also recognized the monoacetylated derivative. In contrast, N¹,N¹²-diacetylspermine did not inhibit spermidine uptake, nor was it incorporated into the cells, indicating the absence of transport systems that recognize N¹,N¹²-diacetylspermine on the apical membranes of LLC-PK₁ cells. These results may be relevant as to our previous observation that the content of diacetylpolyamines in urine is relatively constant, and may explain the excellence of N¹,N¹²-diacetylspermine as a tumor marker.