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Ontogeny of iminoglycine transport in mammalian kidney
Insights
Newborn mammals show inefficient renal tubular absorption of amino acids like proline and glycine. This is due to the absence of high-affinity transport systems, with uptake relying on a low-affinity system.
Area of Science:
- Nephrology
- Developmental Biology
- Amino Acid Transport
Background:
- Renal tubular absorption of amino acids is crucial for nutrient reabsorption.
- Developmental changes in kidney function significantly impact solute transport.
- Proline, hydroxyproline, and glycine are important amino acids handled by the kidneys.
Purpose of the Study:
- To investigate the developmental differences in renal tubular transport of proline, hydroxyproline, and glycine.
- To characterize the transport systems involved in iminoglycine uptake in newborn versus adult mammalian kidneys.
- To explore the underlying mechanisms for reduced initial uptake rates in the postnatal kidney.
Main Methods:
- In vitro analysis of amino acid transport using kidney cortex slices from newborn and mature rats.
- Measurement of initial uptake rates and intracellular concentrations of proline and glycine.
- Assessment of substrate efflux rates from kidney slices.
- Analysis of transport system kinetics at various substrate concentrations.
Main Results:
- Newborn rat kidney cortex slices exhibit reduced initial transport rates for proline and glycine compared to mature kidneys.
- Despite lower initial uptake, newborn slices achieve higher intracellular amino acid concentrations due to decreased efflux.
- The reduced uptake in newborns is attributed to the absence of two high-affinity transport systems present in mature kidneys.
- A single low-affinity system mediates amino acid uptake in the newborn kidney.
Conclusions:
- The iminoglycine transport system in mammalian kidneys undergoes significant developmental changes post-birth.
- The postnatal kidney relies on a low-affinity transport system, while mature kidneys utilize both high- and low-affinity systems.
- Asynchronous development of high-affinity systems suggests independent genetic regulation of iminoglycine transport mechanisms.
Abstract:
Renal tubular absorption of proline, hydroxyproline, and glycine by the newborn of most mammals is inefficient compared to that of the adult. Cortex slices from seven-day-old rat kidney also transport proline and glycine at reduced initial rates compared to mature kidney. Nonetheless, newborn slices achieve higher intracellular concentrations during prolonged incubation; the latter reflects a reduced rate of efflux, a characteristic peculiar to the membrane of postnatal kidney. The postnatal reduction of initial uptake rates is observed clearly only at substrate concentrations in or below the physiological range; it correlates with the absence of two high-affinity systems which normally serve proline and glycine transport independently at these concentrations in mature kidney, in conjunction with a "common" low-affinity system. The low-affinity system alone performs the observed uptake in the newborn kidney. Specific activity of the high-affinity systems for proline and glycine increases asynchronously after birth, suggesting independent genetic control of the three systems for iminoglycine transport in mammalian kidney.