AJP - Gastrointestinal and Liver Physiology, Vol 248, Issue 1 87-G92, Copyright © 1985 by American Physiological Society
Developmental maturation of D-glucose transport by rat jejunal brush-border membrane vesicles
F. K. Ghishan and F. A. Wilson
D-Glucose uptake into jejunal brush-border membrane vesicles was studied in
suckling (2-wk-old), weanling (3-wk-old), and adolescent (6-wk-old) rats.
The purity of the membrane vesicles from all age groups was validated by
the finding that the specific activity of brush-border enzyme markers was
severalfold greater in membrane vesicles compared with corresponding values
in mucosal homogenate. D-Glucose uptake was inversely related to increasing
medium osmolality, indicating that uptake of D-glucose was into the
intravesicular space rather than binding. D-Glucose uptake was sodium
dependent at all age groups; however, the initial uptake at 20 s was
significantly greater in adolescent rats compared with suckling rats. The
addition of valinomycin to KCl-preincubated vesicles in the presence of Na+
gradient resulted in a severalfold increase in D-glucose initial uptake
over Na+ gradient alone, indicating that D-glucose uptake was electrogenic
at all age groups. To delineate the mechanism for the decrease in the
initial uptake in suckling rats, two experiments were performed: 1) an
exchange tracer study that indicated the activity of D-glucose-Na+
transporters was similar in suckling and adolescent rats, and 2) a study
that indicated 22Na uptake, as an indicator for Na+ permeability, was
significantly greater in suckling rats compared with adolescent rats. These
findings suggest that a Na+-dependent, electrogenic D-glucose uptake is
already developed in the suckling period; however, because of the increased
permeability to Na+, the Na+ gradient dissipates faster, resulting in a
decrease in initial uptake.
