Uptake of 2,6-diaminopurine-2-14C by 2,6-diaminopurine-sensitive and -resistant L strain mouse cells grown on plastic discs

Abstract

The short-term uptake of 2,6-diaminopurine-2-14C by 2,6-diaminopurine-sensitive (DAP-s) or -resistant (DAP-r) L cells was studied by means of a "disc sampling" technique. Monolayers of cells were grown on plastic discs which were subsequently incubated for various periods of time in cell growth medium containing 2,6-diaminopurine-2-14C. At 37 °C the uptake of DAP-2-14C by DAP-r cells was relatively linear with respect to the extracellular concentration of DAP-2-14C, whereas the uptake by DAP-s cells was characterized by the phenomenon of saturation. The uptake of DAP-2-14C by DAP-s cells was greatly reduced by lowering the temperature to 4 °C, and a Q10 value of 1.8 was calculated. Under conditions of low temperature and (or) short incubation time, which limited DAP metabolism in DAP-s cells, the uptake of DAP-2-14C by DAP-s and DAP-r cells was similar, suggesting similar permeability. However, the involvement of an enzymatic transport system, as well as the intracellular metabolic enzyme system, in DAP-s cells was not ruled out. The data suggest that permeability is not a major factor in the resistance of L cells to DAP, but the overall uptake of DAP is facilitated by the presence in DAP-s cells of adenine phosphoribosyltransferase, which catalyzes the formation of DAP ribonucleotide, and possibly of an enzymatic transport system, whereas the entry of DAP into DAP-r cells, which lack, or have very low amounts of, adenine phosphoribosyltransferase, appears to be by simple diffusion.