GLUT-1 AND GLUT-2 MESSENGER-RNA, PROTEIN, AND GLUCOSE-TRANSPORTER ACTIVITY IN CULTURED FETAL AND ADULT HEPATOCYTES

To understand glycogenesis in the fetal hepatocyte, we examined glucos e transport in cultured fetal and adult male rat hepatocytes. GLUT-1 m RNA was detected in fetal hepatocytes at isolation but in adult hepato cytes only after culture. GLUT-1 mRNA was more abundant in fetal than in adult hepatocytes (P < 0.005). GLUT-1 protein paralleled its messag e. GLUT-2 mRNA was more abundant in adult than in fetal hepatocytes (P < 0.05), and abundance did not change during culture, but GLUT-2 prot ein was discordantly regulated. There was more GLUT-2 protein in fetal hepatocytes at 45 h (P < 0.025). An Eadie-Hofstee plot of 3-O-methylg lucose transport appeared to have two linear components. One component was presumed to be GLUT-1 [variable Michaelis constant (K-m) approxim ating 6-8 mM, maximal uptake rate (V-max) for fetal vs. adult hepatocy tes 106 vs. 35 nmol.min(-1).mg protein(-1)], and a second was presumed to be GLUT-2 (K-m of 23 mM, V-max for fetal vs. adult hepatocytes 198 vs. 92 nmol.min(-1).mg protein(-1)). Early phosphorylation of 2-deoxy glucose was greater in fetal than in adult hepatocytes, but transport was always greater than phosphorylation. Increased expression of both GLUT-1 and GLUT-2 by fetal hepatocytes permits greater glucose uptake and positions the fetal rat hepatocyte for efficient glycogenesis at l ow plasma glucose concentration.