Transport of monovalent cations by the isolated small intestine of the rat

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Abstract
Everted segments of the small intestine of the rat, taken from both jejunal and ileal regions, were able to transport sodium against an electrochemical gradient by a highly specific mechanism. Other monovalent cations (cesium, potassium, lithium and triethylammonium) moved across the tissue much more slowly than sodium and always in the direction of the electrochemical gradient. Water movement appeared to be passive following the osmotic forces set up by active solute transfer. Both the electrical potential difference across the tissue and the net water transfer fell rapidly when the sodium concentrations in the media were reduced below 120 mm/l. Glucose transport was also responsive to the cation composition of the media; low concentrations of sodium were inhibitory, lithium at 25 mm/l. produced a stimulatory effect, and potassium at 25 mm/l. was inhibitory.