The sodium–glucose cotransport channel

In cotransport, the unfavorable movement of a substance through the membrane is coupled to the favorable transport of another substance.

The sodium–glucose cotransport channel is also presumed to have two possible states
one open only to the outside
one open only to the inside of the cell

Transition to the inside open state is stimulated by glucose binding to E.Na+

Return to the outside-open state occurs upon Na+ release to the inside of the cell.

The sodium gradient from inside to outside provides the driving force for the unfavorable transport of glucose.