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Development of dipeptide transport in rat renal brush border membranes: studies with glycylsarcosine
C Tiruppathi1, V Ganapathy, F H Leibach
1Department of Cell and Molecular Biology, Medical College of Georgia, Augusta 30912-3331.
Insights
Dipeptide-proton cotransport in rat kidneys increases with age, peaking at 42 days. This enhanced transport is linked to greater sodium-hydrogen exchanger activity in adult rats, driving nutrient uptake.
Area of Science:
- Physiology
- Biochemistry
- Renal Biology
Background:
- Dipeptide transport across the renal brush border membrane is crucial for nutrient reabsorption.
- Proton cotransport mechanisms are vital for this process, but their developmental changes are not fully understood.
- The sodium-hydrogen (Na+-H+) exchanger plays a key role in establishing the proton gradient necessary for dipeptide uptake.
Purpose of the Study:
- To investigate the developmental changes in dipeptide-proton cotransport in rat renal brush border membrane vesicles.
- To determine the relationship between age, dipeptide uptake kinetics, and Na+-H+ exchanger activity.
- To compare the activity of nutrient transport systems in suckling versus adult rats.
Main Methods:
- Uptake studies of the dipeptide glycyl-sarcosine in rat renal brush border membrane vesicles across different age groups.
- Kinetic analysis of glycyl-sarcosine transport to assess changes in maximal velocity and affinity.
- Measurement of Na+-H+ exchanger activity in vesicles from suckling and adult rats.
- Assessment of Na+ gradient-driven glucose and amino acid transport.
Main Results:
- Glycyl-sarcosine uptake, characterized by the overshoot phenomenon, increased with age, reaching maximum levels in 42-day-old rats.
- Kinetic studies revealed an increase in maximal velocity of dipeptide transport with age, while affinity remained constant.
- Na+-H+ exchanger activity was significantly higher in adult rats compared to suckling rats.
- Activities of Na+ gradient-driven glucose and amino acid transport systems were also higher in adult rats.
Conclusions:
- Dipeptide-proton cotransport is developmentally regulated in the rat kidney, with enhanced activity in adults.
- Increased Na+-H+ exchanger activity contributes to the augmented proton gradient and thus, enhanced dipeptide transport in adult rats.
- These findings highlight the maturation of renal transport systems responsible for nutrient absorption during postnatal development.
Abstract:
Dipeptide-proton cotransport was studied in rat renal brush border membrane vesicles from animals of different ages, starting at 7 days after birth. In the presence of an inward-directed proton gradient, glycyl-sarcosine uptake exhibited the overshoot phenomenon in all age groups studied. The magnitude of the "overshoot" increased with age and maximum accumulation of glycyl-sarcosine was observed in 42-day-old rat renal brush border membrane vesicles. Kinetic studies with glycyl-sarcosine indicated changes only in maximal velocity without any significant change in the apparent affinity value during the postnatal development of the renal brush border membrane. Since the Na+-H+ exchanger located at the brush border membrane is primarily responsible for the generation of the proton gradient, the driving force for dipeptide transport, we also measured the Na+-H+ exchanger activity in rat renal brush border membrane vesicles from suckling and adult animals. The exchanger activity was significantly greater in the adult rats compared to the suckling rats. In addition, we have confirmed in the present study previous findings from other laboratories that the activities of the Na+ gradient-driven glucose and amino acid transport systems in renal brush border membrane vesicles were higher in the adult than in the suckling rats.