AJP - Gastrointestinal and Liver Physiology, Vol 249, Issue 6 751-G760, Copyright © 1985 by American Physiological Society
D-Glucose transport in piglet jejunal brush-border membranes: insights from a disease model
D. J. Keljo, R. J. MacLeod, M. H. Perdue, D. G. Butler and J. R. Hamilton
We measured glucose transport in jejunal brush-border membrane vesicles
isolated from piglets with acute viral diarrhea, comparing our results with
those from control animals. Characterization of membranes from both study
groups demonstrated comparable purity and integrity. In the presence of an
inwardly directed Na SCN gradient, D-glucose accumulated in control
vesicles to a concentration several times the 60-min equilibrium level.
"Overshooting" uptake was much lower and more gradual in vesicles from 40-h
transmissible gastroenteritis (TGE)-infected pigs compared with control
pigs. Equilibrium kinetic studies, in which gramicidin was used to clamp
membrane potential at zero, demonstrated a pattern of Na-dependent
D-glucose transport in 40-h TGE-infected membranes that differed greatly
from the control pattern. From an Eadie-Hofstee plot of stereospecific
Na-dependent D-glucose uptake into control vesicles, a pattern suggesting
two carrier populations emerged: one with a low-affinity, apparent Km
equaling 52.63 +/- 13.81 mM and the other a high-affinity apparent Km
equaling 3.92 +/- 0.24 mM for D-glucose. In 40-h TGE-infected membranes,
the pattern conformed to a single line, suggesting a homogeneous population
of low-affinity carriers, (Km = 37.03 +/- 1.92 mM), which did not differ
from the low-affinity carriers seen in control animals. We conclude that
the absence of the high-affinity D-glucose carriers in jejunal brush-border
membrane is an important determinant of the defective glucose transport
that characterizes viral diarrhea. Because previous studies have strongly
suggested that in acute TGE diarrhea the epithelium is composed of
relatively undifferentiated crypt-type cells, we speculate that
high-affinity D-glucose carriers are lacking in normal crypt epithelial
cells and that they are incorporated into brush-border membranes of jejunal
enterocytes as the cells differentiate in the course of their migration
from crypt to villus.
