Sodium-dependent sugar transport in the intestine

Abstract

The transport of sugars across the small intestine and across the brush border membrane of the intestinal epithelial cells is dependent on the presence of sodium in the mucosal bathing medium. In the absence of sodium, cellular accumulation, net transmural transport, and unidirectional influx are all inhibited. Furthermore, sodium influx across the brush border is stimulated by the influx of sugar and the increase in sodium influx is coupled to sugar influx in a ratio of 1:1. A model for sugar transport across the brush border has been proposed in which sugar binds to a membrane site, but only in the presence of sodium is the sugar translocated into the epithelial cell. The driving force for sugar transport is postulated to be the electrochemical gradient for sodium and/or other ions across the brush border membrane and not direct input of metabolic energy. Therefore, sodium-dependent sugar transport in the intestine can be considered an example of co-transport.