AJP - Endocrinology and Metabolism, Vol 267, Issue 1 E88-E94, Copyright © 1994 by American Physiological Society
GLUT-1 and GLUT-2 mRNA, protein, and glucose transporter activity in cultured fetal and adult hepatocytes
L. L. Levitsky, Q. Zheng, K. Mink and D. B. Rhoads
Pediatric Endocrine Unit, Massachusetts General Hospital, Boston.
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 hepatocytes only
after culture. GLUT-1 mRNA was more abundant in fetal than in adult
hepatocytes (P < 0.005). GLUT-1 protein paralleled its message. 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 protein 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-methylglucose
transport appeared to have two linear components. One component was
presumed to be GLUT-1 [variable Michaelis constant (Km) approximating 6-8
mM, maximal uptake rate (Vmax) for fetal vs. adult hepatocytes 106 vs. 35
nmol.min-1.mg protein-1], and a second was presumed to be GLUT-2 (Km of 23
mM, Vmax for fetal vs. adult hepatocytes 198 vs. 92 nmol.min-1.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.
