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Phosphate transport by intestinal endoplasmic reticulum during maturation
1Vanderbilt University, Department of Pediatrics, Nashville, Tennessee 37232.
Insights
Phosphate transport into rat jejunal endoplasmic reticulum is energy-dependent and ATP-requiring. Suckling rats exhibit significantly higher phosphate uptake than adolescent rats due to more active phosphate carriers.
Area of Science:
- Cell Biology
- Molecular Biology
- Physiology
Background:
- Phosphate is essential for cellular functions, and its transport mechanisms are critical for maintaining homeostasis.
- The role of the endoplasmic reticulum in intestinal phosphate transport, particularly during development, remains incompletely understood.
Purpose of the Study:
- To investigate and characterize phosphate transport into jejunal endoplasmic reticulum vesicles in suckling and adolescent rats.
- To determine the kinetic parameters and identify factors influencing phosphate uptake in these vesicles.
Main Methods:
- Isolation of jejunal endoplasmic reticulum vesicles from suckling and adolescent rats.
- Utilized a rapid filtration technique to measure phosphate uptake.
- Assessed energy dependence, ATP dependence, pH optimum, and the effect of p-Chloromercuribenzoate.
Main Results:
- Phosphate uptake is an energy-dependent and ATP-dependent process, optimal at pH 7.2.
- p-Chloromercuribenzoate significantly inhibited phosphate uptake, indicating carrier-mediated transport.
- Phosphate uptake rates and carrier activity were significantly higher in suckling rats compared to adolescent rats, with distinct kinetic parameters (Km and Vmax).
Conclusions:
- This study provides the first evidence for a phosphate carrier in the intestinal endoplasmic reticulum of rats.
- The endoplasmic reticulum plays a significant role in intestinal phosphate absorption, with developmental differences observed.
- Enhanced phosphate uptake in suckling rats is attributed to a greater number and/or activity of phosphate carriers.
Abstract:
The transport of phosphate into jejunal endoplasmic reticulum vesicles isolated from suckling and adolescent rats was investigated using a rapid filtration technique. Intestinal endoplasmic reticulum from both ages were enriched with NADPH cytochrome-C-reductase whereas other markers for brush border, basolateral, mitochondrial, and Golgi apparatus were impoverished. Phosphate uptake represented an energy-dependent process as evident by more than 80% decrease in uptake values at 0 degrees C compared to 25 degrees C. Phosphate uptake was ATP dependent in both age groups, however, mean uptake values were significantly greater in suckling rats compared to adolescent rats. pH optimum for uptake was 7.2 p-Chloromercuribenzoate at 100 microM concentration inhibited phosphate uptake by more than 90%. Initial rate of phosphate uptake was linear up to 45 s. Kinetics of phosphate uptake at 30 s showed a Km of 0.7 +/- 0.1 and 0.15 +/- 0.1 suckling and adolescent rats, respectively. Vmax was 1.5 +/- 0.5 and 0.14 +/- 0.01 nmol/mg protein/30 s for both suckling and adolescent rats, respectively. Herein we provide evidence for the first time for the presence of a phosphate carrier in intestinal endoplasmic reticulum of rats. Endoplasmic reticulum of phosphate uptake was significantly greater in suckling rats compared to adolescent rats. This increase in uptake is due to a greater number and activity of phosphate carriers in suckling rats.