Cholera is an important cause of infectious diarrhoea and death. The disease is caused by a toxin produced by the bacterium Vibrio cholerae. The toxin exerts its effect by binding to receptors on small intestinal cells, stimulating production of the second messenger cAMP inside the cells. This opens a chloride channel in the membrane and as a result negatively charged chloride ions are able to move out of the cell. Cholera causes severe diarrhoea which results in severe dehydration and hyponatraemia. Treatment for cholera involves the administration of fluids which replace both water and electrolytes. Use your knowledge of SGLTs to explain why patients do better with oral fluids that contain sodium and glucose than fluids that contain only sodium.

Cholera opens chloride channels in the membrane and as a result negatively charged chloride ions are able to move out of the cell. Positively charged sodium ions follow down the electrical gradient that is created. The high concentration of ions outside the cells makes water leave the cell by osmosis, resulting in severe diarrhoea. Deaths due to cholera have decreased since the introduction of oral rehydration therapy. Oral rehydration therapy involves getting patients to drink a solution with the aim of replacing water and ions that have been lost. The key to successful oral rehydration is for the solution to also contain glucose. Glucose is important because the reabsorption of sodium in the intestinal occurs using a sodium-glucose cotransporter. Sodium won’t be reabsorbed unless glucose is also available for co-transport. As sodium is reabsorbed into the cells, water follows by osmosis.