Sodium-Glucose Cotransport: Indirect Active Transport
Definition
The sodium-glucose cotransporter
The sodium-glucose cotransporter is a protein that moves sodium ions (Na⁺) and glucose molecules together across a plasma membrane into a cell.
- Energy Source: The movement of Na⁺ down its concentration gradient provides the energy needed to transport glucose against its gradient.
- Mechanism: Sodium ions release energy as they move down their gradient, which drives glucose into the cell without directly using ATP.
Applications of Sodium-Glucose Cotransport
- Kidney Function:
- Sodium-dependent cotransport is critical in the proximal tubules of the kidney.
- Here, cells reabsorb glucose from the filtrate to prevent it from being lost in urine.
- Maintaining Gradients:
- Glucose uptake relies on a high Na⁺ concentration outside the cell.
- This gradient is maintained by the sodium-potassium pump, which uses ATP to pump Na⁺ out of the cell while bringing K⁺ in.
In healthy individuals, nearly all glucose is reabsorbed in the proximal tubule, so none is lost in urine.
Indirect Active Transport
- Why “Indirect”?
- Although ATP is required to maintain the sodium gradient, the cotransporter itself does not directly use ATP.
- Instead, energy from Na⁺ movement powers glucose transport.
- Secondary Active Transport:
- The process is termed secondary active transport because the energy comes from the ion gradient established by primary active transport, not from ATP directly.
The sodium-potassium pump is essential for maintaining the sodium gradient that powers SGLT function. Without this pump, glucose absorption would cease.
Theory of KnowledgeHow does the concept of "cooperation" in biological processes, such as sodium-glucose cotransport, parallel ecological relationships like mutualism?
