Mechanisms of transport of p-borono-phenylalanine through the cell membrane in vitro

The mechanisms of transport of p-(dihydroxyboryl)-phenylalanine (BPA) throu gh the cell membrane were investigated in vitro, evaluating especially the systems responsible for the transport of neutral amino acids as potential c arriers for BPA, Rat 9L, gliosarcoma cells and Chinese hamster V79 cells we re exposed to BPA under controlled conditions and in a defined medium that was free of amino acids. The time course of B-10 (delivered by BPA) uptake and efflux was measured under different conditions. To analyze the intracel lular boron content, direct-current plasma atomic emission spectroscopy (DC P-AES) was used after separating the cells from extracellular boron in the cell medium using an oil filtration technique. The dependence of factors su ch as cell type, temperature, composition and concentration of amino acids and specific substrates for amino acid transport systems in the culture med ium or in intracellular compartments on BPA uptake and efflux were studied. The results of this study support the hypothesis that BPA is transported b y the L system and that transport can be further stimulated by amino acids preaccumulated in the cell by either the L or A amino acid transport system . (C) 2000 by Radiation Research Society.