Glucose transport by horse kidney brush borders. I.–Transport properties of brush border membrane closed vesicles.

This research analyzed the transport characteristics of glucose across the brush border membranes of horse kidneys. It demonstrates that these membranes carry out selective, sodium-dependent glucose transport that can be inhibited by phlorizin and is sensitive to osmotic changes.

Methodology and Findings

• The membranes in question were isolated from the cortex of a horse kidney and established as closed right-side out vesicles. These vesicles were found to have selective permeability when tested on sucrose and dextran gradients.
• The glucose transport process was observed and verified by several measures. The vesicles were found to actively accumulate D-glucose, signifying an efficient glucose transport system.

The Transport Process: Characteristics and Effectors

• The rate of uptake and release of D-glucose was found to be higher when a sodium gradient was present, indicating that the D-glucose transport is sodium-dependent. This suggests that sodium ions may play a crucial role in facilitating the transport mechanism.
• D-glucose transport was found to be specific for the D-isomer. Phlorizin, a known inhibitor of glucose transport in the kidneys, was found to impede this transport process, providing further evidence of the mechanism’s function.
• The transportation system showcased saturation kinetics, meaning there’s a maximum rate at which glucose can be transported over time, even with increased glucose concentration.
• The study also found that C-mannose, a stereoisomer of glucose, did not inhibit D-glucose transport, suggesting that the carrier protein involved in the transport is highly specific and does not interact with similar but structurally different sugars.
• Lastly, the researchers discovered the D-glucose uptake is sensitive to osmotic variations, meaning the transport can be affected by changes in pressure or concentration of other particles in the solution.