Biochemical, physiological and pharmacological studies of nutrients uptake have been conducted on a variety of animals using many techniques. There were some differences in results that were often attributed to these techniques. Glucose is one of the most important nutrients in the eukaryotic cells. Integral membrane proteins mediate its movement across the cellular membranes. It is reasonable to expect that this transport system share similarities but also have species differences. With the development of technological advances it has become possible to study this transport in detail. Two families of glucose transporter have been identified: the facilitated-diffusion transporters (GLUT family) driven by the concentration differences across the membrane, and the Na+-dependent glucose transporter (SGLT family) an energy-dependent transport system. Sodium glucose transporters are expressed in bacteria and animal cells, none have yet been found in plants. There is evidence that sugar absorption by the intestine of sea cucumber thyone depends on sodium. In mussels glucose transfer across the mantle cell membrane occurs in conjunction with sodium flow on a shared carrier protein. Cotransport of Na+ and glucose is quantitatively the most important absorptive mechanism in the small intestine in mammals, as illustrated by the success of oral rehydration solutions in diarrhea. It plays a central role in the absorption of glucose and galactose from food. It is also expressed in the proximal renal tubule where it is important for the reabsorption of glucose from the glomerular filtrate. This review focuses on the sodium-glucose cotransporters present in different animals from invertebrate to mammals; we also discuss their role in the control of glucose flux into the different tissues.
Buy this Article