Potassium transport in the human small bowel.

Factors influencing transport of potassium in the human small bowel were studied using perfusion techniques in normal subjects and in patients with ileostomies. In the small intestine of normal subjects and in the ileum of ileostomy patients, potassium is distributed across the mucose in a passive transport process. Potassium transport in the jejunum was influenced to a large degree by solvent drag. The mucosa of the jejunum seems more permeable to potassium than to sodium, and this permeability was apparently unaffected by calcium in the lumen in concentrations of 1.15-7.25 mEq/liter. Potassium transport in the ileum was influenced by luminal sodium concentration, suggesting that this is a passive consequence of the change in electrical potential induced by the change in sodium concentration. In this way, the electrical potential is thought to be a sodium diffusion potential. Therefore, all evidence points to a purely passive behavior of the small intestine toward potassium.