Characteristics of L-glutamine transport in equine jejunal brush border membrane vesicles.

This study investigates how L-glutamine, an amino acid, is transported within the brush border membrane vesicles of horse’s small intestines, or jejunum. The primary transporter system is sodium-dependent and has high-affinity for glutamine. Other amino acids can inhibit it, but changes in pH or use of lithium instead of sodium cannot. A second, sodium-independent transporter has a lower capacity.

Investigation of L-glutamine Transport

• The research primarily focused on characterizing the sodium-dependent transporter system that accounts for L-glutamine uptake in the brush border membrane vesicles of equine jejunum. It is a membrane structure in the horse’s small intestine.
• The investigators verified the vesicle purity by noting a 14- to 17-fold increase in the activity of specific brush border enzyme markers.
• The researchers found that L-glutamine uptake occurs into an osmotically active space, implying that the concentration of particles in a solution influences the uptake.

Details of the Sodium-Dependent Transporter

• Approximately 80% of total glutamine uptake is facilitated by the sodium-dependent transporter, and shows an ‘overshoot’ phenomenon, which is a temporary surge in the uptake rate.
• Kinetic studies showed that the sodium-dependent glutamine transport revealed a single saturable high-affinity carrier. It means that the carrier will be fully saturated at high glutamine concentration and can’t take up any more.
• The Michaelis constant for the sodium-dependent transporter was found to be 519 +/- 90 microM, indicating the concentration at which the transport rate is half the maximum.
• Changes in environmental pH proved to have no substantial impact on glutamine uptake.
• Neither could lithium substitute sodium as a contransporter ion. The analysis also revealed that specific amino acids like histidine, alanine, cysteine, and nonradioactive glutamine resulted in notable inhibition of the sodium-dependent carrier.

Sodium-Independent Transporter

• The study discovered a secondary, sodium-independent transporter, with a considerably lower maximal transport velocity compared to the primary, sodium-dependent one.
• The kinetic analysis of this secondary transporter revealed a Michaelis constant of 260 +/- 47 microM.

Conclusion

• The study suggests that the L-glutamine transport in equine jejunal brush border membrane vesicles is primarily facilitated by the system B transporter, which is sodium-dependent, and to a lesser extent, by a secondary sodium-independent carrier.