Sodium–Glucose Cotransport

Sodium–glucose cotransport is a membrane transport process in which the movement of sodium ions down their electrochemical gradient provides the energy to move glucose into a cell. It is carried out by sodium–glucose cotransporters (SGLTs). In the small intestine, SGLT1 is the principal sodium-dependent transporter responsible for absorbing glucose and galactose across the brush-border membrane of enterocytes .^1,2

Human SGLT1 typically couples the entry of one glucose molecule with two sodium ions. This is an example of secondary active transport because SGLT1 does not directly use ATP. Instead, its energy comes from the sodium electrochemical gradient maintained largely by the sodium–potassium ATPase on the basolateral membrane of the enterocyte. This pump uses ATP to move sodium out of the cell, helping maintain the gradient that drives SGLT1 .^1,2

After glucose enters an enterocyte through SGLT1, it can leave across the basolateral membrane through the facilitative glucose transporter GLUT2 and enter the circulation. Sodium is transported out of the enterocyte by the sodium–potassium ATPase. Coupled sodium and glucose absorption also promotes intestinal water absorption, an important basis of oral rehydration physiology .¹

Sodium–glucose cotransport is distinct from facilitated glucose diffusion. SGLTs couple glucose movement to sodium and can transport glucose against its concentration gradient, whereas GLUT transporters move glucose by facilitated diffusion and do not require sodium cotransport .^1,2