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Developmental maturation of D-glucose transport by rat jejunal brush-border membrane vesicles
Insights
D-glucose uptake in rat jejunum is sodium-dependent and electrogenic from birth. While transporters are functional in suckling rats, increased sodium permeability reduces glucose uptake efficiency.
Area of Science:
- Physiology
- Molecular Biology
- Nutritional Science
Background:
- D-glucose absorption is crucial for infant nutrition.
- The jejunum plays a key role in nutrient uptake.
- Understanding developmental changes in nutrient transport is essential.
Purpose of the Study:
- To investigate the developmental characteristics of D-glucose uptake in rat jejunal brush-border membrane vesicles.
- To determine the sodium dependence and electrogenic nature of D-glucose transport across different age groups.
- To elucidate the mechanisms underlying reduced D-glucose uptake in suckling rats.
Main Methods:
- Isolation and validation of jejunal brush-border membrane vesicles from suckling, weanling, and adolescent rats.
- Measurement of D-glucose uptake under varying osmolality and sodium conditions.
- Assessment of electrogenicity using valinomycin and sodium gradient.
- Exchange tracer studies and 22Na uptake assays to evaluate transporter activity and sodium permeability.
Main Results:
- D-glucose uptake was sodium-dependent and electrogenic in all studied age groups.
- Adolescent rats exhibited significantly higher initial D-glucose uptake compared to suckling rats.
- D-glucose-Na+ transporter activity was comparable between suckling and adolescent rats.
- Suckling rats showed significantly higher sodium permeability than adolescent rats.
Conclusions:
- A functional sodium-dependent, electrogenic D-glucose uptake system is present in the jejunum during the suckling period.
- Increased sodium permeability in suckling rats leads to faster dissipation of the sodium gradient, reducing initial D-glucose uptake.
- These findings highlight developmental adaptations in intestinal nutrient transport.
Abstract:
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.