GLUT-1 and GLUT-2 mRNA, protein, and glucose transporter activity in cultured fetal and adult hepatocytes
Levitsky, L.L.; Zheng, Q.; Mink, K.; Rhoads, D.B.
American Journal of Physiology 267(1 Pt 1): E88-E94
1994
ISSN/ISBN: 0002-9513 PMID: 8048518 Document Number: 438188
To understand glycogenesis in the fetal hepatocyte, we examined glucose transport in cultured fetal and adult male rat hepatocytes. GLUT-1 mRNA was detected in fetal hepatocytes at isolation but in adult hepatocvtes only after culture. GLUT-1 mRNA was more abundant in fetal than in adult hepatocytes (P lt 0.005). GLUT-1 protein paralleled its message. GLUT-2 mRNA was more abundant in adult than in fetal hepatocytes (P lt 0.05), and abundance did not change during culture, but GLUT-2 protein was discordantly regulated. There was more GLUT-2 protein in fetal hepatocytes at 45 h (P lt 0.025). An Eadie-Hofstee plot of 3-O-methylglucose transport appeared to have two linear components. One component was presumed to be GLUT-1 (variable Michaelis constant (K-m) approximating 6-8 mM, maximal uptake rate (V-max) for fetal vs. adult hepatocytes 106 vs. 35 nmol cntdot min-1 cntdot 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 cntdot min-1 cntdot mg protein-1). Early phosphorylation of 2-deoxyglucose 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 low plasma glucose concentration.