TRANSPORT OF L-ARGININE IN CULTURED GLIAL-CELLS

Uptake of radiolabelled L-arginine was studied in four different kinds of glial cultures, in astroglia-rich primary cultures derived from ne onatal rat and mouse brains, in pure murine astrocyte cultures, and in rat glioma cells C6-BU-1. A saturable component of uptake was found i n all cases with K-M values between 15 and 35 mu M and V-max values be tween 0.8 and 2.5 nmol.min(-1) (mg protein)(-1). In addition, in all c ell types a non-saturable component dominated total uptake at high con centrations of extracellular arginine. Rates of uptake of arginine wer e not affected when Naf or Cl- were absent from the incubation buffer. Carrier-mediated uptake of arginine was reduced by depolarizing conce ntrations of K+ and strongly inhibited by an excess of lysine or ornit hine. Histidine, asparagine, glutamine, citrulline, creatine, N-G-nitr o-L-arginine, N-G-monomethyl-L-arginine, or L-canavanine inhibited L-a rginine transport to various degrees. Uptake of arginine was not reduc ed in the presence of serine or alanine, cysteic acid, N-methyl-alpha- aminoisobutyric acid, or 2-aminobicyclo-(2.2.1)-heptane-2-carboxylic a cid. Rates of uptake of arginine were increased when cells had been pr eloaded with lysine. Preincubation of primary cultures, but not glioma cells, with bacterial lipopolysaccharide stimulated transport of argi nine by increasing the V-max value of uptake. This stimulation was dep endent on protein synthesis. The results suggest that, at physiologica l concentrations, arginine is taken up into the glial cells with the h elp of the transport system ''y(+)'' for basic amino acids. In glial p rimary cultures, uptake of arginine appears to be regulated by compoun ds which also exert influence on nitric oxide synthesis. (C) 1994 Wile y-Liss, Inc.