AUTORADIOGRAPHIC STUDY OF SUGAR AND AMINO ACID ABSORPTION BY EVERTED SACS OF HAMSTER INTESTINE

Area of Science:

• Gastroenterology
• Cell Biology
• Molecular Physiology

Background:

• The small intestine absorbs nutrients through specialized absorptive cells.
• Understanding the mechanisms of nutrient transport is crucial for intestinal physiology.

Purpose of the Study:

• To investigate the localization of active transport systems for sugars and amino acids in intestinal absorptive cells.
• To determine the role of the brush border and basal membrane in nutrient transport.

Main Methods:

• Autoradiography of hamster jejunum sections incubated with radiolabeled sugars and amino acids.
• Microdensitometry to quantify intracellular concentrations of absorbed substances.
• Inhibition studies using known transport blockers like phlorizin.

Main Results:

• Absorptive cells accumulated L-valine and L-methionine to high intracellular concentrations (5-50 mM) near the brush border.
• Similar, though less pronounced, concentration "steps" were observed for various sugars.
• Inhibitors blocked concentrative uptake at the luminal border, confirming active transport.
• A concentration "step-down" occurred at the basal pole, suggesting a diffusion barrier or efflux system.

Conclusions:

• Active transport systems for sugars and amino acids are primarily located in the brush border region of intestinal absorptive cells.
• The basal membrane may act as a diffusion barrier and possess a weak inward transport system.