Active alanine transport in isolated brush border membranes

Area of Science:

• Biochemistry
• Molecular Biology
• Physiology

Background:

• Amino acid absorption is vital for nutrient uptake in the small intestine.
• Brush border membranes possess specialized transport systems for amino acids.
• Understanding alanine transport mechanisms is key to comprehending intestinal nutrient handling.

Purpose of the Study:

• To characterize the transport system for L-alanine in rat small intestine brush border membranes.
• To investigate the role of sodium ions (Na+) and other factors in alanine uptake.
• To determine the electrogenic nature and driving forces of L-alanine transport.

Main Methods:

• Isolated brush border membrane vesicles from rat small intestine were used.
• Uptake studies were performed using radiolabeled L- and D-alanine.
• Experiments involved manipulating ion gradients (Na+, Li+, K+, H+) and using specific ionophores (valinomycin, carbonyl cyanide p-trifluoromethoxyphenylhydrazone).

Main Results:

• A stereoselective L-alanine transport system was identified, with faster uptake and release of L-alanine compared to D-alanine.
• Uptake was stimulated by Na+ and Li+ and exhibited saturation kinetics.
• Electrogenic transport was demonstrated, driven by Na+ gradients, and influenced by SCN-, K+/valinomycin, and H+ gradients.

Conclusions:

• The brush border membrane possesses a Na+-dependent L-alanine co-transport system.
• This system plays a significant role in the active absorption of L-alanine against a concentration gradient.
• The transport mechanism is electrogenic, utilizing ion gradients to drive L-alanine uptake.