Perivenous localisation of Na-dependent glutamate transport in perfused rat liver.

Periportal and perivenous hepatocytes differ in their metabolism of blood glutamate (Glu). Uncertainty about the mechanisms of Glu blood-liver exchange led us to characterise, by paired-tracer dilution, a sodium-dependent dicarboxylate transporter (resembling system X-ag) in sinusoidal membranes of perfused rat liver (Vmax = 0.18 mumol Glu/g per min, Km = 0.29 mM Glu). Tracer Glu transport was depressed 65% after necrosis of perivenous hepatocytes by acute CCl4 treatment, indicating that X-ag transporter activity is located mainly in these cells, the sites of glutamine (Gln) synthesis from glutamate and ammonia. Modulation of Glu transport may influence the extent of hepatic Gln release.